When Famke charges her phone

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

Hi Erin,

We can set the time in minutes that Famke used her phone to some variable x. The time she charged it becomes 2x. If she gains 2 percent per minute, then the percentage points she gained in 2x minutes is 2(2x) = 4x. Similarly, the time she lost in percentage points while using her phone for x minutes -5(x). We also know that Famke lost 10 percentage points (-10) after charging and using her phone.

Now we can set up the equation and solve for x, which represents the time in minutes that Famke used her phone:

-10 = 4x-5x

-10 = -1x

x = 10

Thus, Famke used her phone for 10 minutes and charged it for 2(x) = 2(10) = 20 minutes.