A radioactive substance decays at a continuous rate of 15.9 % per day. After 5 days, what amount of the substance will be left if you started with 280 mg?

Question

A radioactive substance decays at a continuous rate of 15.9% per day. After 5 days, what amount of the substance will be left if you started with 280 mg?

(a) First write the rate of decay in decimal form.

r=

(b) Now calculate the remaining amount of the substance. Round your answer to two decimal places.

Answer 1

Hi Sunshine R

If you using y=ab^x

a = 280

x = your time in days

Since you are losing substance at a given rate, your decay rate r or b= (1- 0.159).

(1 - r)=(1 - 0.159) does result in a decimal for your decay rate

There other formulas for Exponential Growth and Decay that you can apply as well.

You can the above a try.

Answer 2

Note that we use this formula since the question specifically asked for continuous decay. Had it mentioned a different time-frame for decay, we would have used the formula y=p_0(1+r)^t. Thanks for watching!