How would I solve this?

"If a radioactive substance has a half life of 14 hours, how long would it take to reach a level of 10%"

I have no idea how to do this, although I think I may have copied it down wrong.

2. Originally Posted by largebabies
How would I solve this?

"If a radioactive substance has a halflife of 14 hours, how long would it take to reach a level of 10%"

I have no idea how to do this, although I think I may have copied it down wrong.

I am not sure it is a "quadratic" function problem.
From what I know, it should be exponential, which has a form $y = ab^t$

Half life just means the time for the intial amount decreased by a half.