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Half-lives of two radioactive elements A...

Half-lives of two radioactive elements A and B are 20 minutes and 40 minutes respectively. Initially, the samples have equal number of nuclei. After 80 minutes, the ratio of decayed numbers of A and B nuclei will be

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`T_(X)=20` min, `T_(Y)=50` min
t=100 min
`N_(X) =N_(0)(1/2)^(t/T_(X))`
`rArr N_(X)/N_(0) =(1/2)^(100/20)`
Similarly, `N_(Y)=N_(0)(1/2)^t/T_(Y) rArr N_(Y)/N_(0)=(1/2)^(100/50)`
Dividing both we get `=N_(Y)/N_(X)=8`
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