Question

If the half life of a substance is 30 days and only 1/8 of it remains, how many days have elapsed?​

Answer 1

The half - life of a substance is 10 days

Explanation:

To determine the half-life of a substance is 30 days and only 1/8 of it remains and to find how many days have elapsed.

We know that, the mass of a substance gets halved while passing every half- life, which means

1 half-life → 1/2 left undecayed

2 half-life → 1/4 left undecayed

3 half-life → 1/8 left undecayed

Here 3 half-life must pass to get 1/8, so we calculate it by

 $\frac{t}{t1/2}$ = 3

we know that 30 days have passed, the half-life of substance is

$\frac{30}{t 1/2}$

t₁.₂ = 30 /3

     =10 days.

Thus the half - life of a substance is 10 days if it has only 1/8 remaining.