Question

What percentage of a material will persist after 80 minutes if it’s half life is 20 minutes?

Answer 1

Suppose the concentration of the substance to be n

After 20 min

n----n/2

After 40 min

n/2----- n/4

After 60 min

n/4-----n/8

After 80 min

n/8----n/16

n/16×100=0.0625×100=6.25%

6.25% of of substance is left

I hope this helps ( ╹▽╹ )

Answer 2

Answer:

The percentage of material that will persist after 80 minutes is 6.25%.

Explanation:

We will solve the question through the following equation,

$N=(\frac{1}{2} )^n\times 100$         (1)

Where,

N=number of material that will persist after "n" half-lives

n=total number of half-lives

Where,

$n=\frac{t}{t_\frac{1}{2} }$      (2)

t=total time

$t_\frac{1}{2}$=half life of the material

From the question we have,

t=80 minutes

$t_\frac{1}{2}$=20 minutes

By substituting the required values in equation (2) we get;

$n=\frac{80}{20}=4$       (3)

By substituting the value of "n" in equation (1) we get;

$N=(\frac{1}{2} )^4\times 100$

$N=\frac{1}{16}\times 100$

$N=0.0625\times 100=6.25\%$

Hence, the percentage of material that will persist after 80 minutes is 6.25%.