Question

Element X is a radioactive isotope such that every 20 years, its mass

decreases by half. Given that the initial mass of a sample of Element X is 410
grams, how long would it be until the mass of the sample reached 270 grams,
to the nearest tenth of a year?

Answer 1

12.1

Explanation:

y=a(1/2)^t/h

270=410(1/2)^t/20

Divide both sides by 410

0.6585365854 = (1/2)^t/20

Log Both sides

Log(0.6585365854) / Log(1/2)

.6026645024= t/20

20 x .6026645024 = t

12.05329005 to the nearest tenth is 12.1 = t