Question

Over the past several months, the water level of a lake has been decreasing by 3% each week. If the highest water level before the decrease started was 520 ft, what was the level at the end of 8 weeks?

Answer 1

y= 407.54654 ft

Explanation:

This is an exponential decay functions

y = ab^x where a is the initial value and b is ( 1 - rate of decay)

a = 520

b = 1- 3%

y = 520 ( 1- .3) ^x

y = 520 ( .97) ^x

We want x to be 8 weeks

y = 520 ( .97) ^8

y= 407.54654 ft