Lesson 7

Multiplication Strategies for Larger Numbers

Est. Class Sessions: 2

Daily Practice and Problems

Teacher Notes
X

TIMS Task

  1. Correct
  2. Wrong; 28; the boys forgot that division and multiplication are the same level and are to be computed at the same time from left to right; 28 ÷ 2 = 14; 14 × 2 = 28.
  3. Wrong; 83; the boys added the 3 to the (6 + 2) before multiplying the (6 + 2) by (5 + 5). Addition in the parentheses comes first to make it 10 × 8 + 3. The multiplication comes next; 80 + 3; the 3 is added last, 83.
  4. Correct
  5. Wrong; 36; as in Question B, division and multiplication are the same level and are to be computed from left to right; 24 ÷ 2 = 12; 12 × 3 = 36.
  6. Wrong; 19; the boys didn't do the multiplication first;
    15 − 6 + 2 × 5 = 15 − 6 + 10 = 19.

V. Using Order of Operations

Mert and Bert solved these problems. They learned the order of operations in school but sometimes they get confused and don't apply it correctly. Check their answers. If the answer is correct, mark it with a large C. If the answer is not correct, solve the problem correctly and tell what the boys did wrong.

  1. 6 + 2 + 4 × 5 = 28
  2. 28 ÷ 2 × 2 = 7
  3. (5 + 5) × (6 + 2) + 3 = 110
  4. 4 × 3 + 10 ÷ 2 = 17
  5. (20 + 4) ÷ 2 × 3 = 4
  6. 15 − 6 + 2 × 5 = 55