If an initial quantity grove or decays at an exponential rate or , then the final amount after a time is given by the following formula . 

If an initial quantity grove or decays at an exponential rate or , then the final amount after a time is given by the following formula .

a.

Find the amount of water used in , where the rate is annually.

World wide water usage in was million gallons.

Since world wide water usage in was million gallons,  .

Time period between and  is years.

Since time period between and  is years, .

Substitute , and in .

.

The amount of water used in is .

Find the amount of water used in , where the rate is annually.

Time period between and  is years.

Since time period between and  is years, .

Substitute , and in .

.

The amount of water used in is .

b.

Find the amount of water used in ,  where the rate is continuously.

Substitute , and in .

.

The amount of water used in is .

Find the amount of water used in ,  where the rate is continuously.

Substitute , and in .

. 

The amount of water used in is .

a.

The amount of water used in is .

The amount of water used in is .

b.

The amount of water used in is .

The amount of water used in is .