Question
Question: If 10% of a radioactive substance decays in every 5 years, then the percentage of the substance that...
If 10% of a radioactive substance decays in every 5 years, then the percentage of the substance that will have decayed in 20 years will be-
A
40%
B
50%
C
65.6 %
D
34.4 %
Answer
34.4 %
Explanation
Solution
= 90% = 0.9 = 
= 
= (0.9)4 = 65.6%
=1 –
= 34.4 %