I think the correct answer is C. Since a=πr², in order to get the area to become 1/4 of what it was previously, the radius needs to be cut in half to make the divide that side by 4. a=π(r/2)²=πr²/4 and will therefore multiply the area by 1/4.

4 0

3 years ago

(Drinking and driving.) Just after Eric had his last drink, the alcohol level in his bloodstream was 0.20 (milligram of alcohol

kykrilka [37]

Here's the formula for exponential decay:

$A = p(1-k)^t$

(where A = new amount, p = principal (starting) amount, k = rate of decay, and t = time)

Let's use what we know and fill in the expression.

$0.08 = 0.20(1-0.47)^t$

And now we solve for t.

$0.08 = 0.20(0.53)^t \\ 0.4 = 0.53^t \\ log0.4=t*log0.53 \\ t = \frac{log0.4}{log0.53} = \boxed{1.44\ hours}$

4 0

3 years ago