Mental Math Strategies

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Mental Math Strategies · Grade 2 · Worksheet 1

1. Liam collected 35 seashells at the beach. His sister Emma found 28 seashells. How many seashells did they collect altogether? Answer: 63 Solution: Identify the number of seashells each person collected. Liam collected 35 seashells. Emma collected 28 seashells.
   Full step-by-step solution

   Step 1: Identify the number of seashells each person collected. Liam collected 35 seashells. Emma collected 28 seashells. Step 2: Understand that "altogether" means we need to find the total number of seashells. To find the total, we add Liam's seashells and Emma's seashells. Step 3: Write the addition equation. 35 + 28 = ? Step 4: Add the numbers. First, add the ones place: 5 + 8 = 13. Write down 3 in the ones place, and carry over 1 to the tens place. Step 5: Add the tens place: 3 (from 35) + 2 (from 28) + 1 (carried over) = 6. Write down 6 in the tens place. Step 6: Combine the digits: The tens place is 6 and the ones place is 3, so the total is 63. Step 7: State the final answer. Altogether, they collected 63 seashells.

2. Emma has 36 crayons in her art box. Her teacher gives her 18 more crayons for a special project. How many crayons does Emma have now? Answer: 54 Solution: Emma starts with 36 crayons She gets 18 more crayons Add the two amounts: 36 + 18 Add the ones place: 6 + 8 = 14 (write 4, carry 1) Add the tens place: 3 + 1 + 1 = 5 Combine: 50 + 4 = 54 The answer is 54.
   Full step-by-step solution

   Step 1: Emma starts with 36 crayons Step 2: She gets 18 more crayons Step 3: Add the two amounts: 36 + 18 Step 4: Add the ones place: 6 + 8 = 14 (write 4, carry 1) Step 5: Add the tens place: 3 + 1 + 1 = 5 Step 6: Combine: 50 + 4 = 54 The answer is 54.

3. 82 - 37 = ? Answer: 45 Solution: Start with 82 - 37. Adjust 37 up to 40 by adding 3. So think of 82 - 40 = 42.
   Full step-by-step solution

   Step 1: Start with 82 - 37. Step 2: Adjust 37 up to 40 by adding 3. So think of 82 - 40 = 42. Step 3: Since we subtracted 3 extra, we need to add 3 back: 42 + 3 = 45. The answer is 45.

4. Emma has 56 crayons in her art box. Her teacher gives her 38 more crayons for a big project. How many crayons does Emma have now? Answer: 94 Solution: Start with Emma's original crayons: 56 Add the new crayons from her teacher: 38 Add the tens: 50 + 30 = 80 Add the ones: 6 + 8 = 14 Combine the tens and ones: 80 + 14 = 94 The answer is 94.
   Full step-by-step solution

   Step 1: Start with Emma's original crayons: 56 Step 2: Add the new crayons from her teacher: 38 Step 3: Add the tens: 50 + 30 = 80 Step 4: Add the ones: 6 + 8 = 14 Step 5: Combine the tens and ones: 80 + 14 = 94 The answer is 94.

5. Noah has a rectangular array of stickers. There are 9 rows of stickers and 7 stickers in each row. How many stickers does Noah have in total? Answer: 63 Solution: There are 9 rows with 7 stickers in each row, so we need to find 9 x 7. Use the 'make a ten' mental math strategy: 9 x 7 = (10 x 7) - (1 x 7). 10 x 7 = 70.
   Full step-by-step solution

   Step 1: There are 9 rows with 7 stickers in each row, so we need to find 9 x 7. Step 2: Use the 'make a ten' mental math strategy: 9 x 7 = (10 x 7) - (1 x 7). Step 3: 10 x 7 = 70. Step 4: 1 x 7 = 7. Step 5: 70 - 7 = 63. Noah has 63 stickers in total.

6. 52 - 27 = ? Answer: 25 Solution: Start with 52 - 27. Adjust 27 up to 30 by adding 3. So think of 52 - 30 = 22.
   Full step-by-step solution

   Step 1: Start with 52 - 27. Step 2: Adjust 27 up to 30 by adding 3. So think of 52 - 30 = 22. Step 3: Since we subtracted 3 extra, we need to add 3 back: 22 + 3 = 25. The answer is 25.

7. 58 + 36 = ? Answer: 94 Solution: Start with 58 + 36 Break 36 into 2 + 34 to make adding easier Add 58 + 2 = 60 Add 60 + 34 = 94 The answer is 94.
   Full step-by-step solution

   Step 1: Start with 58 + 36 Step 2: Break 36 into 2 + 34 to make adding easier Step 3: Add 58 + 2 = 60 Step 4: Add 60 + 34 = 94 The answer is 94.