The total cost of five boxes of pizza is $7 x 5 =$<<7*5=35>>35.
He gave $35 x 1/7 = $<<35*1/7=5>>5 tip to the delivery man.
He spent a total of $35 + $5 = $<<35+5=40>>40 for the pizza and the tip.
The change that he received is $100 - $40 = $<<100-40=60>>60.
#### 60