The exponential function *N* = 500 × 0.64^{t}, where *t* is measured in years, shows the amount, in grams, of a certain radioactive substance present.

*N*(4). (Round your answer to one decimal place.)

*N*(4) =

Explain what your answer means.

(b) What is the yearly percentage decay rate? (Round your answer to one decimal place.)

%

(c) What is the monthly decay factor rounded to three decimal places?

What is the monthly percentage decay rate? (Round your answer to one decimal place.)

%

(d) What is the percentage decay rate per second? (*Note:* For this calculation, you will need to use all the decimal places that your calculator can show. Round your answer to eight decimal places.)