Question

Katie knew that 70 + 70 = 140. Explain how she can use this double to solve 70 + 80.

Answer 1

you would just add 10 to 140

Answer 2

see below

Explanation:

70 + 70 = 140.

We know that 80 is 10 more than 70

the answer to 70+80 must be 10 more than the answer to 70+70 =140

so 140+10 = 150