Question

Power usage is measured in kilowatt-hours, kWh. After 7 a.m., the power usage on a college campus increases at a rate of 21% per hour. Prior to 7 a.m., 15,040 kWh have been used. The university has a daily goal to keep their power usage less than or equal to 100,000 kWh.

Which of the following inequalities can be used to determine the number of hours, t, after 7 a.m. when the power usage on campus will be less than or equal to 100,000?A.
15,040(0.79)t ≤ 100,000
B.
15,040(1.79)t ≤ 100,000
C.
15,040(1.021)t ≤ 100,000
D.
15,040(1.21)t ≤ 100,000

Answer 1

D. 15,040(1.21)t ≤ 100,000

Explanation:

The 15,040 is the prior electricity, and it increases by .21 per hour, and you don't want 100,000

To make an equation, use the simple interest formula (same concept)

Total = Amount(1 + rate) time

fill it out

100,000 >= 15,040(1.21)t

This equation is the same as D so D is the answer