Physics-
General
Easy
Question
The mean lives of a radioactive substance are 1620 years and 405 years for 
-emission and 
-emission respectively. The time during which three fourth of a sample will decay if it is decaying both by -emission and -emission simultaneously.
- 449 years
- 349 years
- 249 years
- 149 years
The correct answer is: 449 years
Total decay constant is 
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