SOLUTION: Urgent request. Can you help me solve this problem: 1) The concentration of salt in Lake Ontario doubles every 7.25 years. If the current levels are 312.5 parts per million, a) F

Algebra ->  Trigonometry-basics -> SOLUTION: Urgent request. Can you help me solve this problem: 1) The concentration of salt in Lake Ontario doubles every 7.25 years. If the current levels are 312.5 parts per million, a) F      Log On


   

Question 204822: Urgent request. Can you help me solve this problem:
1) The concentration of salt in Lake Ontario doubles every 7.25 years. If the current levels are 312.5 parts per million, a) Find an expression for the concentration of salt in Lake Ontario after n years.
b) The concentration levels of salt in the Dead Sea are 10 000 parts per million. How long will it take for the concentration of salt to reach these levels in Lake Ontario?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
1) The concentration of salt in Lake Ontario doubles every 7.25 years.
If the current levels are 312.5 parts per million,
a) Find an expression for the concentration of salt in Lake Ontario after n years.
f(n) = 312.5%282%5E%28n%2F7.25%29%29
:
b) The concentration levels of salt in the Dead Sea are 10 000 parts per million.
How long will it take for the concentration of salt to reach these levels in Lake Ontario?
:
f(n) = 10000
:
312.5%282%5E%28n%2F7.25%29%29 = 10000
:
Divide both sides by 312.5
%282%5E%28n%2F7.25%29%29 = 10000%2F312.5
:
%282%5E%28n%2F7.25%29%29 = 32
:
32 = 2^5 so we can write it:
%282%5E%28n%2F7.25%29%29 = 2^5
therefore
n%2F7.25 = 5
n = 5 * 7.25
:
n = 36.25 yrs
:
:
Check solution on a calc: enter 312.5 * 2%5E%2836.25%2F7.25%29 = 10000