Answer:
Explanation:
We want to know the percentage of the radio active element after 7half life
Let assume the original mass or quantity of the radioactive element is No
After first half life it remains No/2
Second half life No/4
Third half life No/8
Fourth half life No/16
Fifth half life No/32
Sixth half life No/64
Seventh half life No/128
So after the seventh half life the radioactive element has decay to No/128
Then, the that remain is
The remaining amount / Original amount × 100
%remain = (No/128 / No) × 100
No cancel No
%remain = 100/128
%remain = 0.78%
