Question

When Famke charges her phone, it gains 2 percentage points each minute. When Famke uses her phone, it loses 5 percentage points each minute. Once, Famke used her phone for some time, and then charged it for twice the amount of time she used it. In the end, her phone lost 10 percentage points. How long did Famke use her phone and how long did she charge it?

Answer 1

Gains 2 percent per minute = 0.02m
Loses 5 percent per minute = -0.05m
Charged two times the usage
Loss of 10
-0.10 = 2(0.02)m - 0.05m
-0.10 = 0.04m- 0.05m
-0.10 = -0.01m
m = 10 minutes

She used her phone 10 minutes and charged it 20 minutes

Check:
20 min x 0.02 = + 40 percent
10 min x -0.05 = - 50 percent
40 - 50 = -10 percent