Question

The mass m(t) remaining after t years from 90-gram sample of a radioactive element is given by m(t)=90e^-0.3t. When will the mass remaining equal 9 grams? Round your answer to the nearest hundredth of a year.

Answer 1

a. 2.30 years
b. 7.68 years
c. 0.12 years
d. 3.33 years
e. 0.13 years

Answer 2

I substituted the t for each one of the answers but i dont get 9 with any of them

Answer 3

9 = 90e^(-0.3t)

1/10 = e^(-0,3t)

ln (1/10) = -0.3t

t = ln(10) / 0.3

t= 7.67528364

therefore t = 7.68

Answer 4

Thanks mate