Question

Isandro and Yvette each have a calculator. Yvette starts at 100 and subtracts 7 each time. Isandro on the other hand, starts at zero and adds 3 each time. If they press the keys at the same time, will their displays ever show the same number? if so, what is the number?

Answer 1

Yvette = 100-7x
Isandro = 0+3x

0+3x = 100 - 7x
0+3x+7x = 100 - 7x +7x
10x = 100
x = 10
So on the 10th time they have the same number, which is 30.