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Half lives of two isotpers X and Y are k...

Half lives of two isotpers X and Y are know to be `2xx10^(9)` years and `4xx10^(9)` years of these isotopes and currntly the meterical has 20% of X and Y 80% by number on the plabnet. The current age of the planet is

A

`2xx10^(9)` years

B

`4xx10^(9)` years

C

`6xx10^(9)` years

D

`8xx10^(9)` years

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The correct Answer is:
D
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