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A sum of money placed at compound interest doubles itself in 5 years in how many years it would to 8 times of itself at the same rate of interest?

Correct answer: C. 15 years

  • A. 7 years
  • B. 10 years
  • C. 15 years
  • D. 20 years

Explanation

If the amount doubles in 5 years, it becomes four times in 10 years and eight times, which is 2^3, in 15 years. This uses repeated doubling at the same compound rate. Students may choose 10 years by confusing eight times with four times the original amount.

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About Percentages

Percentages express a quantity as parts per hundred and support calculations involving increases, decreases, discounts, commissions, taxes, and successive changes. Questions require distinguishing percentage change from percentage points and identifying the original value when a final value and its percentage change are given.

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