# The pollution in a normal atmosphere is less than 0.01%. Due to leakage of a gas from a factory, the pollution is increased to 20%. If everyday 80% of the pollution is neutralized , in how many days the atmosphere will be normal( #log_2 = 0.3010#)?

##
A) 3

B) 4

C) 5

D) 6

A) 3

B) 4

C) 5

D) 6

##### 1 Answer

#### Explanation:

The pollution percentage is at

This means that each day, we multiply the pollution percentage by

To solve it, we will first divide both sides by

Now we can take a logarithm on both sides. Which logarithm we use doesn't really matter, we're just after the logarithm properties. I'm going to pick the natural logarithm, since it's present on most calculators.

Since

If we divide both sides, we get: