The relation between number of half-lives and the amount of sample that remained is expressed as:
(1/2)^n = x
So, given is 7.
To find x, we will change the equation with 7:
(1/2)^n = x
(1/2)^7 = x
0.5^7 = x
0.0078125 = x
0.0078125 x 100% = x
x = 0.78125
Therefore, 0.78 % of a radioactive species would be created as daughter material after seven half-lives.
