Students use number bonds and manipulatives to represent part-part-whole relationships (e.g., placing 1 penny in one small circle and 2 in the other, then counting the whole as 3). The lesson explicitly asks students to find a missing part when given the whole and one part (example: 4 in the large circle and 1 in a small circle, so the other small circle must be 3). Students use base-10 unit blocks to show combinations that make a whole (4+1, 3+2, etc.) and count the whole when two parts are given.

Students compare two sets and compute "how many more" using counters and an abacus (Activity 5), answering questions like "How many more are in the first row?" and finding numeric differences (e.g., 5 vs. 3 → 2). Students complete a template sentence in Activity 6 ("_____ is _____ more than _____") and may use manipulatives or a number line to determine which number is greater and by how much. Students also practice arranging numbers and filling in missing numbers in a sequence that reinforces understanding of numeric order (Activity 4).

Students practice composing numbers using 5 in Activity 8: they move abacus beads and say phrases like "2 combines with 5 to make 7" and complete the "Combining With 5" sheet by adding beads to reach target totals. The Number Chants explicitly state decompositions ("6 is 5 and 1," "7 is 5 and 2," etc.), and students draw or add beads to make specified totals on activity pages.

Students complete number bonds and 'What's Missing?' problems that present equations such as 10 = 6 + ( ) and similar missing-addend tasks (Activity 7). Students roll dice to create parts and place totals in the whole circle, modeling part-part-whole relationships and finding the missing part or whole (Activity 5). Students use fish and story problems to combine groups and fill in unknown totals to 10 (Activities 8, 9, 10).

Students are asked to solve the cookie problem ("I need 10 cookies. Right now I only have 5 cookies. How many more do I need?"), which requires finding the unknown addend. Students are prompted to find "1 more than 5" when counting coins and to show 13 cents using 2 nickels (students must add 3 pennies), which requires determining a missing quantity to reach a total. The "Showing Cents" activity asks students to make given cent amounts in two ways, encouraging students to combine known parts to produce a total.

Activity 3 (Number Bonds to 20) has students draw a number card (11–20), write that number in the large circle, and use the abacus to find and write the missing number in the small circle (finding the addend that, with 10, makes the given total). Activity 4 and the "Showing 11-20" sheet ask students to interpret base-10 block and abacus/rod representations and write the correct total (finding the sum from given parts). Activity 2 (coin tasks) has students show numbers like 12 or 17 cents in multiple additive combinations, so students practice decomposing numbers into sums.

Students create and answer "Do the Math!" cards that include number-bond questions such as "Which number bonds with 5 to make 10?" and a number-bond diagram with missing parts. Students cut out, sort, fill in blanks on, and generate their own cards (including number-bond cards) and then must answer those cards during gameplay to remain on a space.

Students practice counting on a number line and linking those counts to adding and subtracting in Activity 1 and Activity 2, where they count up and back to find larger and smaller numbers. The Student Activity Page asks students to record a Starting Number, a Roll of the Die, the result for Counting Up (start + roll) and the result for Counting Back (start - roll), with the example 10, 3, 13, 7. Students are prompted to make jumps on the number line and to write the sums and differences after repeated die rolls.

The Skills list explicitly states students should "Determine the unknown whole number in an addition or subtraction equation relating three whole numbers." Activity 3 (Animal Addition) presents equations with blanks (for example, "_ + 2 = _" and "_ + _ = 7") that require students to fill in missing addends or sums using pictured quantities. Activities 4 and 5 have students use an abacus and number bonds to find missing addends (for example, writing 6+3= ____ and showing 1 and finding 9 to make 10).

Students solve explicit missing-addend equations in Activity 2, where they represent and write problems such as 4 + ? = 10 and are given practice problems 5 + ? = 7, ? + 3 = 5, and 2 + ? = 8 using counters, drawings, and an abacus. The Skills list states "Understand subtraction as an unknown addend problem," and Activity 4 has students represent subtraction with manipulatives and write number sentences like 10 - 4 = 6 and 10 - 8 = 2. The Student Activity Page contains subtraction problems with blanks (e.g., 7 - __ = __) that require students to fill missing numbers and compute results.

Students add sets of items (including problems with three addends) using one-dollar counters in the Shopping activities and are told that adding three numbers uses the same process as adding two. In the How Much Change? activity, students compute change after a $10 purchase (for example, if purchases total $4 the child gives back $6) and record purchases on a whiteboard while using play bills to make the correct change. The activities ask students to add multiple numbers within 20 and to subtract from 10 when making change, providing practice with sums and differences.

Students record counts of Skittles and write totals in Activity 2, answering "How many green and purple Skittles did you draw altogether?", which requires adding two whole numbers (4 + 3 = 7). Students also answer "How many more yellow Skittles are there than purple ones?", which requires finding the difference between two counts (7 - 3 = 4). Students write totals from tally marks and count groups of five in Activities 1 and 4, practicing combining and comparing whole-number quantities.

Students add category counts to find totals (e.g., the question "How many birds did the birdwatcher see in all?" and "How many people in all responded to the survey?"). Students place and count Skittles by color and record the counts on a pictograph, which requires summing items across categories. Students use number strips and are asked to identify and point to specific larger numbers, reinforcing whole-number counting and aggregation.

Students count and combine categories to find totals (for example, questions ask "How many Skittles would you have if you put all the red ones and yellow ones together?" and "How many orange, yellow, and green Skittles did you pick in all?"). Students add two categories when asked "How many games and puzzles do you have altogether?" and find differences when asked "How many more spotted fish than striped fish are there?" and "How many more seahorses than sharks are there?". Students also create bar graphs and use the numbers on the y-axis to compute totals and differences from the displayed data.

Students solve the "Who Has the Most?" word problems by computing Marta's number (Beth has 8, Marta has 2 more), Jack's number (Jack has 3 fewer than Beth), and Chase's number (Chase has 4 fewer than Marta). The lesson tells students to use addition or subtraction to answer those questions and asks them to record the resulting counts for each person. Students then use those computed numbers to complete a table or create a graph showing the quantities.

The Skills section explicitly lists "Determine the unknown whole number in an addition or subtraction equation relating three whole numbers." Activity 2 ("Something's Missing") has students complete number sentences by finding the missing number (e.g., 5 + ___ = 10; ___ - 3 = 1; ___ + 9 = 9; 6 - 6 = ___; 10 - 4 = ___; 4 + ___ = 8). The activity allows use of counters, an abacus, or a number line and asks students to create and read their own number sentences, practicing unknowns in different positions.

Students roll a die and name the number that combines with the rolled number to make 10, which requires finding a missing addend (for example, 3 + ? = 10). Students divide 10 counters into three groups, write the corresponding addition sentence (for example, 3 + 3 + 4 = 10), place an = and the sum, and record addition sentences on the "Making 10 with Three" sheet. Students play games and story problems that require adding three whole numbers to determine the total (for example, adding 3 + 4 + 2 to find 9).

Students create addition sentences that make 10 in Activity 3 by cutting and gluing numbers into boxes to show pairs that sum to 10, and they practice turn-around facts (e.g., 1+9 and 9+1). In Activity 4 students draw number cards 11–20 and create number bonds by choosing addends that produce the given sum, using counters and the abacus to check (e.g., making 11 as 5 and 6). In Activities 1, 2, and 6 students write addition sentences (including three-number sums with dice) and compute missing results by using manipulatives and the abacus, and they are asked to point to addends and sums when reading sentences aloud.

Students fill in missing addends on the "What 5 Makes" activity (e.g., 5 + __ = 7 and __ + 5 = 10), which requires determining an unknown number in an addition equation. Students create and complete addition sentences with dominoes and on the whiteboard (e.g., write 8+5 and complete it) and use the abacus and counters to find sums and turn-around facts. The Addition Concentration activities require matching addition expressions with their sums, reinforcing finding the unknown total in addition problems.

Students practice adding three numbers and looking for known sums (Activity 1 shows 4 + 6 + 3 and 5 + 2 + 3 and asks students to decompose to 10 + 3 and 5 + 5). In the Party Paper Chains activities, students must determine unknown counts from totals (for example, a chain with 16 links that has 10 green links requires finding the other color count, and a 15-link chain in three colors with equal numbers requires finding each color's number). The Number Collection wrap-up asks students to show 15 in as many ways as they can, including addition sentences with two and three addends.

The Skills section explicitly lists "Determine the unknown whole number in an addition or subtraction equation relating three whole numbers." Students are asked to show the number 18 in as many ways as possible, including addition sentences with two and three addends. Multiple activities require students to write subtraction sentences and find missing differences (egg carton subtraction examples, the laminated number line tasks, the Filling the Boxes worksheet with empty answer boxes, Domino War differences, and the deck-of-cards wrap-up asking for differences).

The Skills section explicitly lists "Determine the unknown whole number in an addition or subtraction equation relating three whole numbers" and says to use addition and subtraction within 20 with unknowns in all positions. In Activity 1 students are asked to create number sentences from word problems (e.g., "How many more..." and the zookeeper needing 10 elephants) and then find the answers, including a problem with three addends (5 + 8 + 6). Activity 3 asks students to compute change (pay $10 and find the change), which requires solving subtraction equations with an unknown, and Connect 3 gives many subtraction problems within 20 for students to solve.

The skills list and activities explicitly ask students to determine missing numbers and to create addition and subtraction sentences with a given number as the sum or as the first number (e.g., select a card and create 10 + 2 = 12, 6 + 6 = 12, 12 − 1 = 11). The Missing Number Sign prompts students to fill in "10 combines with ______ to make the missing number" and to produce two 2-addend addition sentences, two 3-addend addition sentences, and two subtraction sentences with the missing number as the first number. The materials instruct students to use counters and an abacus and to divide a set (for example, 11 counters) into 3 groups to create three addends that sum to the target number.

Students complete the "Math Facts Quiz 3" where they write answers to addition and subtraction problems (e.g., 1 - 0 = __, 1 + 4 = __), practicing finding unknown results. Students flip number cards 1–10 and state both the sum and the difference for each pair, practicing addition and subtraction with whole numbers. Students play Domino War and compute totals on dominoes to practice adding two whole numbers up to 10.

Students practice addition and subtraction facts with flashcards and timed quizzes (the Math Facts Quiz 4 presents problems such as 3 + 3 = __ and 6 - 2 = __). The skills list explicitly states that students will 'Add and subtract within 20, demonstrating fluency for addition and subtraction within 10.' Students also play web games (Alien Addition and Minus Mission) set to ranges within 1–10 to build fact recall.

Students practice addition and subtraction facts through an online game and a ‘Math Facts Quiz 5' worksheet in which they fill in the blank answers for expressions such as 5+1=, 10-8=, and 6-6=. The Skills list explicitly states that students will add and subtract within 20 and demonstrate fluency for addition and subtraction within 10, and students are reminded of mental strategies (turn-around facts, adding/subtracting 1, etc.). The worksheet and timed quiz require students to compute unknown results for basic addition and subtraction problems.

Students are asked to determine "how many more" to reach a target number (for example, when counting groups of ten: "If she has 4 baggies of objects, how many more will she need to get to 10? (6)") and are prompted with questions such as "How many do you have now?" and "How many more do you need to get to 100?". Students complete number sequences from 91 to 100 on a number grid and use counting-by-10s to show totals, which requires them to find missing quantities to reach a given total.

Students use number bonds, an abacus, and ten rods to find missing addends (for example, finding 7 to complete 3 + 7 = 10 and finding 70 to complete 30 + 70 = 100). Students complete a 'Making 100' worksheet where each problem is of the form X + ___ = 100 and they fill in the blank to make the equation true. Activities prompt students to write and read number sentences such as 3+7=10 and 30+70=100 aloud, and to use manipulatives to determine the missing addend.

Students fill in missing numbers in sequences (e.g., exercises like 50, __, 40 and longer sequences such as 10, __, 30, __, 50) and complete the "What's missing?" boxes on the activity pages. Students use base-10 blocks and an abacus to add 10 and subtract 10 from given numbers and then color or circle the resulting numbers on the 1–120 number grids. Students are asked to name and read numbers that are 10 more or 10 less (for example, identifying 65 and 45 as 10 more/less than 55).

Students write and compute addition sentences with blanks for sums (for example, 10+30= (40) and the student activity page example 20+30= __). Students roll dice to create multiples of ten and then add them, recording the two addends and the resulting sum on the activity sheet. Students perform subtraction problems such as 40-20= and 60-30= using base-10 blocks or an abacus to find the difference and complete matching exercises that pair number sentences with their sums or differences.

Students practice finding sums and differences of whole numbers, especially multiples of ten: the whiteboard prompts (3+3=6 and 30+30=60) and the ‘5(-)2= 50(-)20=' prompt ask students to compute missing differences. In Activity 2 students cut and match cards with expressions (for example 40+20=, 90-40=) to their sums or differences, and may use base-10 blocks or an abacus to find those results. The 10 More / 10 Less activities have students compute numbers that are 10 more or 10 less, reinforcing addition and subtraction by tens.

Students complete a "Multiples of 10 Number Bonds" activity in which they fill the two smaller circles with multiples of 10 that add to a given total (examples: 80, 50, 30, 70). Students practice finding sums of two multiples of 10 (for example, 20+30, 30+30, 60+10) using an abacus and base-10 blocks, thereby determining unknown sums. Students also solve subtraction problems with multiples of 10 (for example, 60-40) and draw number cards to write subtraction number sentences and find the differences.

Students complete multiple worksheets that have blank boxes for sums (e.g., UFO problems and student activity pages where students fill in answers to addition sentences like 5 + 60 = __ or 21 + 40 = __). One problem explicitly asks students to find how many more coins are needed to make 40 when there are 20 coins, which requires solving 20 + ? = 40 (finding a missing addend). Students are instructed to use base-10 blocks, an abacus, or a place-value mat to find and check answers, supporting hands-on work with unknown addends.

Students practice computing sums in multiple activities: in Activity 1 they use an abacus and base-10 blocks to combine 13 and 6 to find 19, and they compute several two-digit plus one-digit addition sentences. In Activity 2 students match addition sentences to their sums in a concentration game, and the Student Activity Pages provide many addition problems for students to solve. In Wrapping Up students are asked to write three number sentences that have a given number (for example, 14) as their sum, creating pairs of addends that make the target total.

Students are explicitly asked to determine missing addends in Activity 3 ("What's Missing?") where they fill blanks such as 52 + □ = 60, □ + 25 = 30, 71 + □ = 80, and 37 + ___ = 40 using base-10 blocks and an abacus. Student Activity Pages and the answer key show multiple addition problems with missing addends and a matching activity (e.g., 32 + 8, 28 + 2) that require students to identify correct sums. Students are prompted to write number sentences (for example 35 + 5 = 40) and to explain their thinking while checking answers with manipulatives.

Students write and complete number sentences with a blank for the sum (for example, 37+4=____, 19+6=____, 25+8=____, 56+6=____) and use base-10 blocks and an abacus to find and record the sums. Students create addition equations from spinner results (for example, 24+9=___) and use manipulatives to compute and write the answers. Students sort given addition equations into true and false and explain how they found the totals, showing engagement with the equal sign and verifying equations.

Students fill in blanks on the "Go Fish! Numbers" sheet to find missing target sums when addition sentences are provided. Students produce missing addition sentences when a target and one addend are given (e.g., completing an addition sentence to make the target). Students use base-10 blocks and an abacus to compute sums and then write addition sentences on game cards and match equivalent addition representations.

Students draw number cards 1–10 and name the number that combines with the drawn number to make 10 (e.g., draw 3, say "seven"). In the Wrapping Up activity students flip tens cards (10, 20, ..., 100) and say the number that adds to the shown number to make 100 (e.g., flip 60, say "forty"). The Smoothie Math activity directs students to play the "Facts to Make 100 (Multiples of 10)" option, reinforcing finding the missing addend for totals of 100.