Sum multiplies at CI: rate or time to reach another multiple

This type of question, asked 4 times: 12 Sep 2025 S1, 21 Sep 2025 S2, 22 Sep 2025 S1, 23 Sep 2025 S3. All 4 questions below, oldest first.

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Question 1
12 Sep 2025 S1
60 $An amount is said to double in 5 years with compound interest. How many years will it take for the amount to grow to 8 times its original value?$
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Question 2
21 Sep 2025 S2
52 $A sum of money invested at compound interest amounts to twice itself in 4 years. In how many years will it become 8 times itself?$
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Question 3
22 Sep 2025 S1
51 $A sum of money becomes three times itself in 3 years at compound interest. What is the rate of interest?$
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Question 4
23 Sep 2025 S3
51 $A sum of money doubles itself at compound interest in 15 years. In how many years will it become eight times?$
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Question 1