Mental Math Within 20

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Answer Key & Explanations

Mental Math Within 20 · Grade 2 · Worksheet 3

1. Jordan is collecting seashells. Jordan has 16 shells. Jordan finds 43 more on the beach. How many shells does Jordan have in all? Answer: 59 Solution: Start with 16 shells. Find 43 more: 16 + 43 = 59. Jordan has 59 shells in all.
   Full step-by-step solution

   Step 1: Start with 16 shells. Step 2: Find 43 more: 16 + 43 = 59. Jordan has 59 shells in all.

2. A baker had 75 cookies in the morning. She baked 24 more cookies in the afternoon. How many cookies does she have now? Answer: 99 Solution: Start with the 75 cookies from the morning Add the 24 cookies baked in the afternoon Add the ones place: 5 + 4 = 9 Add the tens place: 70 + 20 = 90 Combine the results: 90 + 9 = 99 The baker now has 99 cookies.
   Full step-by-step solution

   Step 1: Start with the 75 cookies from the morning Step 2: Add the 24 cookies baked in the afternoon Step 3: Add the ones place: 5 + 4 = 9 Step 4: Add the tens place: 70 + 20 = 90 Step 5: Combine the results: 90 + 9 = 99 The baker now has 99 cookies.

3. A rectangular garden has 7 rows of flowers. Each row has 8 flowers. How many flowers are there in total? Answer: 56 Solution: There are 7 rows of flowers. Each row has 8 flowers. To find the total, multiply the number of rows by the number of flowers in each row: 7 × 8 7 × 8 = 56 There are 56 flowers in total.
   Full step-by-step solution

   Step 1: There are 7 rows of flowers. Step 2: Each row has 8 flowers. Step 3: To find the total, multiply the number of rows by the number of flowers in each row: 7 × 8 Step 4: 7 × 8 = 56 Step 5: There are 56 flowers in total.

4. 82 - 47 = ? Answer: 35 Solution: Start with 82 - 47 Since you cannot subtract 7 from 2 in the ones place, regroup 1 ten from the tens place. 1 ten equals 10 ones. After regrouping, you have 7 tens and 12 ones (2 ones + 10 ones = 12 ones).
   Full step-by-step solution

   Step 1: Start with 82 - 47 Step 2: Since you cannot subtract 7 from 2 in the ones place, regroup 1 ten from the tens place. 1 ten equals 10 ones. Step 3: After regrouping, you have 7 tens and 12 ones (2 ones + 10 ones = 12 ones). Step 4: Subtract the ones: 12 - 7 = 5 Step 5: Subtract the tens: 7 - 4 = 3 Step 6: Combine the tens and ones: 3 tens and 5 ones is 35 The answer is 35.

5. Lily and Lily are playing a card game. Lily has 41 points. Lily needs 24 more points to win. How many points does a player need to win the game? Answer: 65 Solution: Lily has 41 points. Add the points needed: 41 + 24 = 65. A player needs 65 points to win.
   Full step-by-step solution

   Step 1: Lily has 41 points. Step 2: Add the points needed: 41 + 24 = 65. A player needs 65 points to win.

6. Noah has 32 toy cars in his collection. For his birthday, his aunt gives him 25 more toy cars. How many toy cars does Noah have now? Answer: 57 Solution: Noah starts with 32 toy cars He receives 25 more toy cars Add the two amounts together: 32 + 25 Add the ones: 2 + 5 = 7 Add the tens: 30 + 20 = 50 Combine the results: 50 + 7 = 57 The answer is 57.
   Full step-by-step solution

   Step 1: Noah starts with 32 toy cars Step 2: He receives 25 more toy cars Step 3: Add the two amounts together: 32 + 25 Step 4: Add the ones: 2 + 5 = 7 Step 5: Add the tens: 30 + 20 = 50 Step 6: Combine the results: 50 + 7 = 57 The answer is 57.

7. Sophia and Sophia are playing a card game. Sophia has 73 points. Sophia needs 8 more points to win. How many points does a player need to win the game? Answer: 81 Solution: Sophia has 73 points. Add the points needed: 73 + 8 = 81. A player needs 81 points to win.
   Full step-by-step solution

   Step 1: Sophia has 73 points. Step 2: Add the points needed: 73 + 8 = 81. A player needs 81 points to win.