Question

The percent y (in decimal form) of battery power remaining x hours after you turn on a cell phone is y=−0.02x+0.60. What is the battery power when you turn on the phone? How long after you turn on the phone does the battery last?

Answer 1

• 60%
• 30 hours

Explanation:

The fraction remaining at turn-on is found by setting x = 0.

y = -0.02·0 +0.60 = 0.60 = 60%

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The number of hours the battery will last is found by setting y = 0.

0 = -0.02x +0.60

0 = -x + 30 . . . . . . . multiply by 50

x = 30 . . . . . . . . . . . add x

The battery will last 30 hours after you turn on the phone.