Mental Math Strategies

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Answer Key & Explanations

Mental Math Strategies · Grade 2 · Worksheet 3

1. A rectangular garden is 12 meters long and 8 meters wide. What is the perimeter of the garden? Answer: 40 Solution: We have a rectangular garden with a length of 12 meters and a width of 8 meters. We need to find the perimeter, which is the total distance around the garden.
   Full step-by-step solution

   Step 1: Understand the problem We have a rectangular garden with a length of 12 meters and a width of 8 meters. We need to find the perimeter, which is the total distance around the garden. Step 2: Recall the formula for the perimeter of a rectangle The perimeter P of a rectangle is given by: P = 2 × (length + width) Step 3: Substitute the given values into the formula Length = 12 meters Width = 8 meters So, P = 2 × (12 + 8) Step 4: Perform the addition inside the parentheses 12 + 8 = 20 Step 5: Multiply by 2 P = 2 × 20 = 40 Step 6: State the final answer The perimeter of the garden is 40 meters.

2. Emma has 38 crayons in her art box. Her teacher gives her 24 more crayons for a class project. How many crayons does Emma have now? Answer: 62 Solution: Start with Emma's original crayons: 38 Add the new crayons from her teacher: 24 Add the tens: 30 + 20 = 50 Add the ones: 8 + 4 = 12 Combine the tens and ones: 50 + 12 = 62 The answer is 62.
   Full step-by-step solution

   Step 1: Start with Emma's original crayons: 38 Step 2: Add the new crayons from her teacher: 24 Step 3: Add the tens: 30 + 20 = 50 Step 4: Add the ones: 8 + 4 = 12 Step 5: Combine the tens and ones: 50 + 12 = 62 The answer is 62.

3. A square garden has a fence around it. Each side of the garden is 15 meters long. What is the total length of the fence? Answer: 60 Solution: A square has 4 sides that are all the same length. Each side is 15 meters long. To find the total length of the fence, which is the perimeter, add the lengths of all four sides: 15 + 15 + 15 + 15.
   Full step-by-step solution

   Step 1: A square has 4 sides that are all the same length. Step 2: Each side is 15 meters long. Step 3: To find the total length of the fence, which is the perimeter, add the lengths of all four sides: 15 + 15 + 15 + 15. Step 4: 15 + 15 = 30, and 30 + 15 = 45, and 45 + 15 = 60. The total length of the fence is 60 meters.

4. Ethan had 58 toy cars. Ethan gave 14 cars to a friend. How many toy cars does Ethan have now? Answer: 44 Solution: Start with 58 toy cars. Subtract 14 cars that were given away: 58 - 14 = 44.
   Full step-by-step solution

   Step 1: Start with 58 toy cars. Step 2: Subtract 14 cars that were given away: 58 - 14 = 44. The answer is 44.

5. Emma sees a pattern of tiles on the floor. There are 7 rows of tiles, and each row has 9 tiles. How many tiles are there in total? Answer: 63 Solution: There are 7 rows with 9 tiles in each row. This means we need to find 7 groups of 9. Think of 7 x 9.
   Full step-by-step solution

   Step 1: There are 7 rows with 9 tiles in each row. This means we need to find 7 groups of 9. Step 2: Think of 7 x 9. One way to do this mentally is to use a fact you know: 7 x 10 = 70. Step 3: Since 9 is one less than 10, 7 x 9 is the same as 7 x 10 minus one group of 7. Step 4: 7 x 10 = 70. Then subtract 7: 70 - 7 = 63. The total number of tiles is 63.