Question

Suppose the half-life of an element is 10 years. How many half-lives will it take before only about 6% of the original sample remains?

Answer 1

You don't need to worry about the 10 year bit with this question. Just grab a calculator and divide 100/2, then the answer to that (50) by 2 etc and keep dividing by 2 until you get down to 6.25.

The answer ends up being 4 half lives :)

If you don't understand what a half life is please let me know :)

Answer 2

Answer:

40.59 years

Explanation:

Use the decay law of radioactivity

$N = N_{0}e^{-\lambda t}$

Where, λ is the decay constant

λ = 0.6931 / T

where, T is the half life

λ = 0.6931 / 10 = 0.06931 per year

So, N = 6% of N0

$0.06 = e^{-0.06931\times t}$

By solving we get

t = 40.59 years