Select the correct answer.

Question

William recorded data to determine the relationship between the time usage, x, and the percentage of charge left on his mobile phone, y. He graphed the data and drew the line of best fit. The equation of the line of best fit is y = -10x + 100. About how many hours will it take for the phone lose its charge completely?
A.
about 5 hours
B.
about 10 hours
C.
about 20 hours
D.
about 22 hours
E.
about 24 hours

Answer 1

Since the equation is y = -10x + 100, when y (percentage of charge left) equals 0, we can solve for x (time usage):
0 = -10x + 100
10x = 100
x = 10
Therefore, it will take about 10 hours for the phone to lose its charge completely. The answer is B.