Multiple choice

At a certain rate of interest sum become 8 times itself in 14 years. In how many years will it become 16 times itself? एक निश्चित साधारण ब्याज की दर से एक धनराशि 14 वर्षों में स्वयं की 8 गुनी हो जाती है। कितने वर्षों में यह राशि खुद की 16 गुनी हो जायेगी?

  1. 24.75

  2. 28

  3. 30

  4. 32.5
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C Correct answer
Explanation

Let principal be P and rate be r%. In simple interest, amount = P(1 + rt/100). In 14 years, amount = 8P, so P(1 + 14r/100) = 8P. This gives 14r/100 = 7, so r = 50%. To become 16 times: P(1 + 50t/100) = 16P, so t/2 = 15, giving t = 30 years.

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