Question

Fine the nuber of half lives elapsed before which 93.75% of a radioactive sample has decayed

Answer 1

Answer:

Let number of half lives be n .

Assume initial concentration was 100 from which 93.75 decayed or 100 - 93.75 = 6.25 left .

So after n half lives remaining sample will be

$\frac{100}{ {2}^{n} } = 6.25 \\ \\ {2}^{n} = \frac{100 \times 100}{625} = 16 \\ \\ n = 4 \: half \: lives$

Answer 2

Answer:

100/2n =6.25

2n100×100/625 =25

4 half lives