Analyzing Functions in Context

It's legal for Elisabeth to drive if the concentration of alcohol in her blood is under

0.02 % .

To find the time when this happens we can substitute

y = 0.02

into the function, and solve for

x .

y = 0.13 - 0.011 x

y = 0.02

0.02 = 0.13 - 0.011 x

Solve for

x

LHS - 0.02 = RHS - 0.02

0 = 0.11 - 0.011 x

LHS + 0.011 x = RHS + 0.011 x

0.011 x = 0.11

LHS / 0.011 = RHS / 0.011

x = \frac{0 . 1 1}{0 . 0 1 1}

\frac{a}{b} = \frac{a \cdot 1 0 0 0}{b \cdot 1 0 0 0}

x = \frac{1 1 0}{1 1}

CalcQuotCalculate quotient

x = 10

The alcohol level has dropped to

0.02 %

10

hours after midnight. Thus, Elisabeth must wait until

10

o'clock to legally drive.

Analyzing Functions in Context 1.7 - Solution