Question

an element with mass of 630 grams decays by 18.8% per minute. How much of the element is remaining after 7 minutes.

Answer 1

146.63 grams.

Explanation:

The mass percent that remains after every minute is 100%-18.8 = 81.2% of the initial mass. This means after 1 minute the mass remaining is

`630*0.812`

After 2 minutes, the mass reaming is

`(630*0.812)*0.812`

After 3 minutes

`(630*0.812*0.812)*0.812`

so we see the general pattern: the grams remaining after
`m` minutes are

`\boxed{ 630 (0.812)^m}`

Now after 7 minutes the grams remaining are

`630(0.812)^7=146.63`

146.63 grams.