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Half lives of two radioactive nuclei A and B are 10 minutes and 20 minutes, respectively, If initially a sample has equal number of nuclei, then after 60 minutes, the ratio of decayed numbers of nuclei A and B will be :

1. 9 : 8
2. 1 : 8
3. 8 : 1
4. 3 : 8

Correct answer: 9 : 8

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