Question

Veronica has to multiply 398 x 18. She says she can multiply 400 X 18 and then take

away one group of 18.

Write an expression that shows Veronica's thinking

Answer 1

See below. Veronica's thinking is incorrect. I've included what she is thinking, but the correct thinking is more useful, as noted below.

Explanation:

398 is 2 less than 400. Veronica needs to remove two groups of 18.

I don't know what Veronica is thinking, other than:

(398 x 18) = (400*18 - 18)

She should be thinking:

(398 x 18) = (400 x 18) - (2*18). The "2" is for the two extra groups of 18 that she will have when multiplying 400 x 18, instead of 398 x 18.