Question

An element with mass 140 grams decays by 21.6% per minute. How much of the element is remaining after 20 minutes, to the nearest 10th of a gram?

Answer 1

The answer to this question is 1.1 grams

Answer 2

Answer:The mass of the remaining element = 1.1 grams .

Explanation:

Exponential equation of decay :
`y=A(1-r)^x` ... (i), where A = initial value , r= rate of decay in decimal , x= time.

As per given : Initial mass : A= 140 grams

Rate of decay : r= 21.6% per minute= 0.216 per minute.

x= 20 minutes

Substitute values in (i) , we get

`y=140(1-0.216)^(20)\\\\=140(0.784)^(20)=1.0775794222\approx1.1\text{ gram}`

Hence, the mass of the remaining element = 1.1 grams .