Mental Math Within 20

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Answer Key & Explanations

Mental Math Within 20 · Grade 2 · Worksheet 1

1. Mere has 38 stickers. Mere gives away 31 stickers to a friend. How many stickers does Mere have left? Answer: 7 Solution: Start with 38 stickers. Give away 31 stickers: 38 - 31 = 7. Mere has 7 stickers left.
   Full step-by-step solution

   Step 1: Start with 38 stickers. Step 2: Give away 31 stickers: 38 - 31 = 7. Mere has 7 stickers left.

2. Sam has 82 stickers. Sam gives away 11 stickers to a friend. How many stickers does Sam have left? Answer: 71 Solution: Start with 82 stickers. Give away 11 stickers: 82 - 11 = 71. Sam has 71 stickers left.
   Full step-by-step solution

   Step 1: Start with 82 stickers. Step 2: Give away 11 stickers: 82 - 11 = 71. Sam has 71 stickers left.

3. Noah has 32 toy cars in his collection. For his birthday, he receives 25 more toy cars from his friends. How many toy cars does Noah have in total 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 place: 2 + 5 = 7 Add the tens place: 30 + 20 = 50 Combine the results: 50 + 7 = 57 Noah has 57 toy cars in total.
   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 place: 2 + 5 = 7 Step 5: Add the tens place: 30 + 20 = 50 Step 6: Combine the results: 50 + 7 = 57 Noah has 57 toy cars in total.

4. Noah has 42 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: 67 Solution: Noah starts with 42 toy cars. He receives 25 more toy cars. To find the total, add the two numbers: 42 + 25.
   Full step-by-step solution

   Step 1: Noah starts with 42 toy cars. Step 2: He receives 25 more toy cars. Step 3: To find the total, add the two numbers: 42 + 25. Step 4: Add the ones place: 2 + 5 = 7. Step 5: Add the tens place: 4 + 2 = 6. Step 6: Combine the tens and ones: 60 + 7 = 67. The answer is 67.

5. 67 + 28 = ? Answer: 95 Solution: Start with 67 + 28 Break 67 into 60 + 7 and 28 into 20 + 8 Add the tens: 60 + 20 = 80 Add the ones: 7 + 8 = 15 Combine the results: 80 + 15 = 95 The answer is 95.
   Full step-by-step solution

   Step 1: Start with 67 + 28 Step 2: Break 67 into 60 + 7 and 28 into 20 + 8 Step 3: Add the tens: 60 + 20 = 80 Step 4: Add the ones: 7 + 8 = 15 Step 5: Combine the results: 80 + 15 = 95 The answer is 95.

6. A baker made 56 chocolate chip cookies and 38 oatmeal raisin cookies. How many cookies did the baker make in total? Answer: 94 Solution: The baker made 56 chocolate chip cookies and 38 oatmeal raisin cookies. Add the tens first: 50 + 30 = 80 Add the ones: 6 + 8 = 14 Combine the tens and ones: 80 + 14 = 94 The baker made 94 cookies in total.
   Full step-by-step solution

   Step 1: The baker made 56 chocolate chip cookies and 38 oatmeal raisin cookies. Step 2: Add the tens first: 50 + 30 = 80 Step 3: Add the ones: 6 + 8 = 14 Step 4: Combine the tens and ones: 80 + 14 = 94 Step 5: The baker made 94 cookies in total.

7. 76 + 29 = ? Answer: 105 Solution: Add the ones: 6 + 9 = 15 Write down the 5 in the ones place and carry over the 1 to the tens place. Add the tens: 7 + 2 = 9, then add the carried-over 1: 9 + 1 = 10 Write down the 10 in the tens and hundreds places.
   Full step-by-step solution

   Step 1: Add the ones: 6 + 9 = 15 Step 2: Write down the 5 in the ones place and carry over the 1 to the tens place. Step 3: Add the tens: 7 + 2 = 9, then add the carried-over 1: 9 + 1 = 10 Step 4: Write down the 10 in the tens and hundreds places. Step 5: Combine the hundreds, tens, and ones: 100 + 0 + 5 = 105 The answer is 105.

8. Liam has 24 stickers in his collection. His friend Emma gives him 15 more stickers for his birthday. How many stickers does Liam have now? Answer: 39 Solution: Liam starts with 24 stickers. Emma gives him 15 more stickers. To find the total number of stickers Liam has now, we add the stickers he received to the stickers he already had.
   Full step-by-step solution

   Liam starts with 24 stickers. Emma gives him 15 more stickers. To find the total number of stickers Liam has now, we add the stickers he received to the stickers he already had. Step 1: Write the addition problem. 24 + 15 Step 2: Add the numbers. First, add the ones place: 4 + 5 = 9. Then, add the tens place: 2 + 1 = 3. Step 3: Combine the results. The total is 39. So, Liam now has 39 stickers.

9. Ethan and Ethan are playing a card game. Ethan has 45 points. Ethan needs 30 more points to win. How many points does a player need to win the game? Answer: 75 Solution: Ethan has 45 points. Add the points needed: 45 + 30 = 75. A player needs 75 points to win.
   Full step-by-step solution

   Step 1: Ethan has 45 points. Step 2: Add the points needed: 45 + 30 = 75. A player needs 75 points to win.

10. Olivia and Olivia are playing a card game. Olivia has 54 points. Olivia needs 45 more points to win. How many points does a player need to win the game? Answer: 99 Solution: Olivia has 54 points. Add the points needed: 54 + 45 = 99. A player needs 99 points to win.
    Full step-by-step solution

    Step 1: Olivia has 54 points. Step 2: Add the points needed: 54 + 45 = 99. A player needs 99 points to win.