## Pre-cal homework help not just answer but how to do it too

Complex numbers, rational functions, logarithms, sequences and series, matrix operations, etc.
AlejandroDeLaPreCal
Posts: 1
Joined: Wed Mar 19, 2014 12:29 am
Contact:

### Pre-cal homework help not just answer but how to do it too

This exercise uses the radioactive decay model.

The half-life of cesium-137 is 30 years. Suppose we have a 128-g sample.

(a) Find a function that models the mass remaining after t years. (Round rate r to three significant figures.)

(b) How much of the sample will remain after 120 years? (Round your answer to one decimal place.)
g

(c) After how long will only 4 g of the sample remain? (Round your answer to the nearest whole number.)
yr

anonmeans
Posts: 84
Joined: Sat Jan 24, 2009 7:18 pm
Contact:

### Re: Pre-cal homework help not just answer but how to do it t

This exercise uses the radioactive decay model.
The half-life of cesium-137 is 30 years. Suppose we have a 128-g sample.
So P = 128.
(a) Find a function that models the mass remaining after t years. (Round rate r to three significant figures.)
What is half of 128? This is A. This is how much you have at t = 30. Plug these into the equation (A = Pe^{rt}) and solve for r.
(b) How much of the sample will remain after 120 years? (Round your answer to one decimal place.)
Use the P they gave you, the r you just found, and the t they give you for this part. Plug them into the equation and solve for A.
(c) After how long will only 4 g of the sample remain? (Round your answer to the nearest whole number.)
Use the P they gave you, the r you found, and the A they give you for this part. Plug them in and solve for t.

If you get stuck, please write back showing what you've done. Thanks.