College

Solve the problem.

The function [tex]f(x) = 200(0.5)^{x / 50}[/tex] models the amount in pounds of a particular radioactive material stored in a concrete vault, where [tex]x[/tex] is the number of years since the material was put into the vault. Find the amount of radioactive material in the vault after 140 years. Round to the nearest whole number.

A. 156 pounds
B. 29 pounds
C. 280 pounds
D. 36 pounds

Answer :

To find the amount of radioactive material left in the vault after 140 years, we can use the provided function:

[tex]\[ f(x) = 200(0.5)^{x/50} \][/tex]

Here, [tex]\( x \)[/tex] is the number of years since the material was put into the vault. We want to find [tex]\( f(140) \)[/tex].

1. Substitute [tex]\( x = 140 \)[/tex] into the function:

[tex]\[ f(140) = 200(0.5)^{140/50} \][/tex]

2. Calculate the exponent:

[tex]\[ 140/50 = 2.8 \][/tex]

3. Calculate the power of 0.5:

[tex]\[ (0.5)^{2.8} \][/tex]

4. Multiply by the initial amount:

[tex]\[ f(140) = 200 \times (0.5)^{2.8} \][/tex]

5. Round to the nearest whole number:

After evaluating the expression, the function gives us approximately 28.72 pounds. When we round 28.72 to the nearest whole number, we get 29 pounds.

Therefore, the amount of radioactive material in the vault after 140 years is approximately 29 pounds.