Question

The mean lives of a radioactive substance are $1620$ years and $405$ years for $\alpha$ -emission and $\beta$ -emission respectively. The time during which three-fourth of a sample will decay if it is decaying both by $\alpha$ -emission and $\beta$ -emission simultaneously is

• A. 339 years
• B. 449 years
• C. 559 years
• D. 669 years

Answer 1

Answer: (B)

Correct answer is (b) 449 years