Question

After 11 year there will be ? g of a radioactive substance

Answer 1

Initially= 14g

9 years= 7gr

11 years ?

Initial grams - 9 years grams = Number of grams used

14 gr - 7gr= 7gr

Then we have to divide 7 grams by 9 years and we will know how many grams are used per year.

`\begin{gathered} (7)/(9)=\text{ 0.778 grams per year} \\ \end{gathered}`

Then, in 11 years they will use:

0,778 x 11 years = 8.556 grams

Therefore, to know how much radioactive substance is left we have to subtract the initial grams and the grams used after 11 years. So,

14 grams - 8.556 grams = 5.444 grams left.