At simple interest, a sum becomes twice itself in 6 years. In how many years will it become four times itself?

12 yearsCorrect answerYour answer18 yearsCorrect answerYour answer24 yearsCorrect answerYour answer30 yearsCorrect answerYour answer

Show the answer and explanation

CorrectNot quiteAnswer B

Correct answer: B

Twice itself means the interest in 6 years is P.
Four times itself means the interest needed is 3P.
Simple interest grows evenly, so 3P needs $3 \times 6 = 18$ years.

Worth noting

12 years is compound-interest thinking (doubling twice). 24 years multiplies 6 by 4, forgetting that the principal itself is already one of the four parts.

Concept: Multiples of a sum at simple interest
Typical timeTypical: 50 s
Your timeYours: —

The rule this testsSimple interest

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At simple interest, a sum becomes twice itself in 6 years. In how many years will it become four times itself?

Explanation