Question

10. BATTERY LIFE The battery life of a certain cell phone starts at 8 hours. The battery life decreases at an annual rate of 30%.

a. Write a function that represents the battery life y after x years.

b. After how many years will the battery life of a cell phone be 2 hours? Round to the nearest tenth if necessary.

Answer 1

Below

Explanation:

30 % loss means 70 % remains (.7)

y = 8 (.7)^x = battery life after 'x' years

2 = 8(.7)^x solve for 'x'

2/8 = .7^x LOG both sides

log.25 / log.7 = x = ~ 3.9 years