Tripling under simple interest — Aptitude Question
Tripling under simple interest: In how many years will a sum triple itself at 10% per annum simple interest? Answer and worked solution on CodeKairo.
- Topic: Simple & Compound Interest
- Section: Quantitative Aptitude
- Difficulty: Medium
- Time target: 50 seconds
Question
In how many years will a sum triple itself at 10% per annum simple interest?
Options
- 10
- 15
- 20
- 25
Show the answer and the worked solution
Correct answer: C. 20
Worked solution
- To triple, SI = 2P, so R × T = 200.
- T = 200 ÷ 10 = 20 years.
Answer: 20.
The idea
Becoming n times needs R × T = 100(n − 1). Reading 'triple' as 300 instead of 200 is the standard error.
Shortcut. At 10% the interest adds one more P every 10 years: 2P at year 10, 3P at year 20.
Common trap. 10 — that is when the sum doubles (100% interest); tripling needs 200% interest, twice as long.
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