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Mental Math Within 20

Grade 2 · Mathematics · Worksheet 2

  1. A rectangle is drawn on a grid. It has 4 rows of squares and 6 squares in each row. How many total squares are inside the rectangle?
    Answer: ______________
  2. Look at the pattern: ★ ★ ★ ★ ★ | ★ ★ ★ ★ ★ | ★ ★ ★ ★ ★. Each group has 5 stars. How many stars are there in total? Answer: ______________
  3. 52 + 39 = ? Answer: ______________
  4. Maya has 97 stickers. Maya gives away 46 stickers to a friend. How many stickers does Maya have left? Answer: ______________
  5. 42 + 39 = ? Answer: ______________
  6. A rectangle is drawn with 4 rows of circles. Each row has 6 circles. How many circles are there in total?
    Answer: ______________
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Answer Key & Explanations

Mental Math Within 20 · Grade 2 · Worksheet 2

  1. A rectangle is drawn on a grid. It has 4 rows of squares and 6 squares in each row. How many total squares are inside the rectangle? Answer: 24 Solution: The rectangle has 4 rows Each row has 6 squares To find the total squares, multiply rows by squares per row: 4 × 6 4 × 6 = 24 The answer is 24.
    Full step-by-step solution

    Step 1: The rectangle has 4 rows Step 2: Each row has 6 squares Step 3: To find the total squares, multiply rows by squares per row: 4 × 6 Step 4: 4 × 6 = 24 The answer is 24.

  2. Look at the pattern: ★ ★ ★ ★ ★ | ★ ★ ★ ★ ★ | ★ ★ ★ ★ ★. Each group has 5 stars. How many stars are there in total? Answer: 15 Solution: Count the number of groups: There are 3 groups separated by vertical lines. Each group has 5 stars. Multiply the number of groups by the number of stars in each group: 3 × 5 = 15.
    Full step-by-step solution

    Step 1: Count the number of groups: There are 3 groups separated by vertical lines. Step 2: Each group has 5 stars. Step 3: Multiply the number of groups by the number of stars in each group: 3 × 5 = 15. The answer is 15.

  3. 52 + 39 = ? Answer: 91 Solution: Start with 52 + 39 Notice that 39 is close to 40. Add 1 to 39 to make it 40, and subtract 1 from 52 to keep the total the same: (52 - 1) + (39 + 1) = 51 + 40 Add 51 + 40 = 91 The answer is 91.
    Full step-by-step solution

    Step 1: Start with 52 + 39 Step 2: Notice that 39 is close to 40. Add 1 to 39 to make it 40, and subtract 1 from 52 to keep the total the same: (52 - 1) + (39 + 1) = 51 + 40 Step 3: Add 51 + 40 = 91 The answer is 91.

  4. Maya has 97 stickers. Maya gives away 46 stickers to a friend. How many stickers does Maya have left? Answer: 51 Solution: Start with 97 stickers. Give away 46 stickers: 97 - 46 = 51. Maya has 51 stickers left.
    Full step-by-step solution

    Step 1: Start with 97 stickers. Step 2: Give away 46 stickers: 97 - 46 = 51. Maya has 51 stickers left.

  5. 42 + 39 = ? Answer: 81 Solution: Start with 42 + 39 Notice that 39 is close to 40. Add 1 to 39 to make it 40: 42 + 40 = 82 Since we added 1 extra, we need to subtract 1 from our result: 82 - 1 = 81 The answer is 81.
    Full step-by-step solution

    Step 1: Start with 42 + 39 Step 2: Notice that 39 is close to 40. Add 1 to 39 to make it 40: 42 + 40 = 82 Step 3: Since we added 1 extra, we need to subtract 1 from our result: 82 - 1 = 81 Step 4: The answer is 81.

  6. A rectangle is drawn with 4 rows of circles. Each row has 6 circles. How many circles are there in total? Answer: 24 Solution: There are 4 rows of circles. Each row has 6 circles. To find the total, multiply the number of rows by the number of circles in each row: 4 × 6 4 × 6 = 24 The answer is 24.
    Full step-by-step solution

    Step 1: There are 4 rows of circles. Step 2: Each row has 6 circles. Step 3: To find the total, multiply the number of rows by the number of circles in each row: 4 × 6 Step 4: 4 × 6 = 24 The answer is 24.