What is the half-life and how long would it take to decay to 90% of the original amount?

Question

A sample of a radioactive substance decayed to 94% of its original amount after a year. (Round your answers to two decimal places.)

(a) What is the half-life of the substance?

 yr

(b) How long would it take the sample to decay to 90% of its original amount?

Answer 1

(a) 0.94 = e^k

Solve for k

(b) 0.50 = e^kt

Substitute k, solve for t

(c) 0.90 = e^kt

Substitute k, solve for t