Question

If 10% of a radioactive material decays in 5 days, then the amount of original material left after 20 days is approximately-

• A. 60%
• B. 65%
• C. 70%
• D. 75%

Answer 1

Answer: (B)

65%

Answer 2

A.P₂= = $\left( \frac { 90 } { 100 } \right) ^ { 20 / 5 }$

A.P₂ = $\left( \frac { 9 } { 10 } \right) ^ { 4 }$ 100%