Question

A substance decays so that the amount A of the substance left after t years is given by:

A = A0 · (0.9)t,

where A0 is the original amount of the substance. What is the half-life (the amount of time that it takes to decay to half the original amount) of this substance rounded to the nearest tenth of a yea

Answer 1

help

Answer 2

6.6 years
7.5 years
6.1 years
5.6 years

Answer 3

those are the answers

Answer 4

A = A0 · (0.9)^t

At a substance's half life, the final amount A equals (1/2)A0

so substituting (1/2)A0 for A on the left side of the equation:

(1/2)A0 = A0 · (0.9)^t

cancel out A0 from both sides, then solve for t