Question

Ripley told his mom that multiplying whole numbers by multiples of 10 was easy because you just count zeros in the factors and put them in the product. He used these two examples to explain his strategy.

7,000 × 600 = 4,200,000
(3 zeros) (2 zeros) (5 zeros)

800 × 700 = 560,000
(2 zeros) (2 zeros) (4 zeros)

Ripley’s mom said his strategy will not always work. Why not? Give an example.

Answer 1

She is right, it won´t always work.

Explanation:

Hi, in the examples this tactic works because the first numbers, when multiplied, don´t equal 10 (7x6=42 and 8x7=56). If you multiply both numbers and give you 10, you will have to add another zero to the final number and the trick would crash.

Example:

200 x 500 = 100,000

(2 Zeros) (2 zeros) (5 zeros)

Best of luck.