Question

Martin had 7 pounds of grapes left, and he gave away 2/5 of them. Explain how to use compatible numbers to estimate the amount of grapes he gave away.

Answer 1

Answer: 14/35
7-2/5=
7/7 -3/5=
35/35-21/35=
14/35

Answer 2

2/5 is close to 1/2, and it is easy to find 1/2 of 7 mentally. Half of 7 is 3.5, so Martin gave away about 3.5 pounds.