← Quantitative Aptitude

Compound Interest — Questions with Solutions

5 solved Compound Interest questions from Quantitative Aptitude, as asked in SSC CGL and other SSC exams. Read the answer and explanation below, then practise the full set in the practice section.

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Q1. An amount is said to triple in $6$ years with compound interest. How many years will it take for the amount to grow to $27$ times its original value?

एक राशि चक्रवृद्धि ब्याज पर $6$ वर्षों में तिगुनी हो जाती है। मूल राशि को $27$ गुना होने में कितने वर्ष लगेंगे?

  1. A. 18
  2. B. 19
  3. C. 20
  4. D. 21

Solution

Amount triples ($3^1$) in $6$ years. $27$ times is $3^3$. Time $= 6 \times 3 = 18$ years.

Q2. A sum becomes $7,200$ in $2$ years and $8,640$ in $3$ years at compound interest. What is the original principal?

कोई राशि चक्रवृद्धि ब्याज पर $2$ वर्षों में $7,200$ रुपये और $3$ वर्षों में $8,640$ रुपये हो जाती है। मूलधन क्या है?

  1. A. 4,800
  2. B. 5,000
  3. C. 5,200
  4. D. 5,500

Solution

Rate $= \frac{8640 - 7200}{7200} = 20\%$. Principal $= \frac{7200}{(1.2)^2} = 5000$.

Q3. Find the compound interest on $12,000$ at $8\%$ per annum for $2$ years $9$ months, interest compounded annually.

$12,000$ रुपये पर $8\%$ वार्षिक दर से $2$ वर्ष $9$ महीने का चक्रवृद्धि ब्याज ज्ञात कीजिए, जबकि ब्याज वार्षिक रूप से संयोजित होता है।

  1. A. 2,456
  2. B. 2,598
  3. C. 2,712
  4. D. 2,837

Solution

Amount $= 12000 \times (1 + 0.08)^2 \times (1 + 0.08 \times \frac{9}{12}) = 12000 \times 1.1664 \times 1.06 = 14836.9$. Interest $= 14836.9 - 12000 \approx 2837$.

Q4. Find the compound interest on 9,500 at 11% p.a. for 2 years 6 months, compounded annually.

9,500 रुपये पर 11% प्रति वर्ष की दर से 2 वर्ष 6 महीने के लिए वार्षिक रूप से संयोजित चक्रवृद्धि ब्याज ज्ञात कीजिए।

  1. A. 2,848.72
  2. B. 2,798.25
  3. C. 2,850
  4. D. 2,950.50

Solution

Amount = $9500 \times (1 + \frac{11}{100})^2 \times (1 + \frac{5.5}{100})$ (since 6 months is half year, rate is 5.5%). Amount = $9500 \times 1.2321 \times 1.055 = 12348.72$. CI = $12348.72 - 9500 = 2848.72$.

Q5. If the amount at the end of the 4th year and 5th year on a certain principal at compound interest is 24,000 and 26,400 respectively, find the rate of interest per annum.

यदि चक्रवृद्धि ब्याज पर एक निश्चित मूलधन पर चौथे वर्ष और पांचवें वर्ष के अंत में मिश्रधन क्रमशः 24,000 और 26,400 है, तो प्रति वर्ष ब्याज दर ज्ञात कीजिए।

  1. A. 8%
  2. B. 9%
  3. C. 10%
  4. D. 11%

Solution

The interest earned in the 5th year is on the amount at the end of the 4th year. Interest = $26400 - 24000 = 2400$. Rate = $\frac{2400}{24000} \times 100 = 10\%$.