Chapter 11, Problem 7STP

To determine

Find the percent of the original contaminants will be removed from the air.

Answer to Problem 7STP

Option D is correct.

Explanation of Solution

Given:

An air filters claims to remove 90% of the contaminants in the air each time air is circulated through the filter. If the same volume of air is circulated through the filter three times, what percent of the original contaminants will be removed from the air?

4 Options are: A: 0.1%, B: 0.01%, C: 99.99%, D: 99.9%

Calculation:

After first circulation, the contaminants left in air are $(100-90)=10\%$

After second circulation only $(10-90\%·10)\%=1\%$ will be left cause 90% of the remaining 10% will get removed.

After the third circulation only $(1-90\%·1)\%=0.1\%$ will be remain.

So, $(100-0.1)\%=99.9\%$ contaminants will get removed from the air after 3 circulations

Thus, Option D is correct.