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About Compound Interest — Class 9 ICSE

Solve advanced compound interest problems including growth, depreciation, and installments. This topic is part of the ICSE Class 9 mathematics syllabus (chapter: Chapter 2). On this page you can practice 60 questions across three difficulty levels — 20 easy, 20 medium, and 20 hard — each with a visual step-by-step solution, plus a timed 35-question mastery test with a live leaderboard. Worked examples and sample questions from the topic are below.

What you'll learn in Compound Interest

  • Simple Interest Recap
  • Understanding Compound Interest
  • The Compound Interest Formula
  • Compounding for Different Periods
  • Applications and Summary

Interactive lesson · about 20 minutes · checkpoint question after every unit

Compound Interest — solved examples for Class 9 ICSE

Example 1easy

What is the formula for compound interest?
  1. A)A = P(1 + r/100)^n
  2. B)A = P + Prn/100
  3. C)A = P x r x n
  4. D)A = P(1 - r/100)^n

Step-by-step solution

  1. The compound interest formula is:
    A=P(1+r/100)nA = P(1 + r/100)^n
  2. Where A = Amount, P = Principal, r = rate per annum, n = number of years.

Answer: A = P(1 + r/100)^n

Example 2medium

A sum of Rs 20000 is borrowed at 8% per annum compounded annually. What amount is to be paid after 3 years?
  1. A)Rs 24000
  2. B)Rs 25194.24
  3. C)Rs 24883.20
  4. D)Rs 25000

Step-by-step solution

  1. Amount:
    A=20000(1+8/100)3A = 20000(1 + 8/100)^3
  2. Step by step:
    A=20000x1.08x1.08x1.08A = 20000 x 1.08 x 1.08 x 1.08
  3. Calculate:
    A=20000x1.259712=Rs25194.24A = 20000 x 1.259712 = Rs 25194.24

Answer: Rs 25194.24

Example 3hard

A man borrows Rs 20000 at 12% CI. He repays Rs 8000 at the end of the first year and Rs 9000 at the end of the second year. How much must he pay at the end of the third year to clear the debt?
  1. A)Rs 9292.48
  2. B)Rs 9500
  3. C)Rs 8800
  4. D)Rs 10000

Step-by-step solution

  1. After year 1:
    20000x1.12=22400.Afterpayment:22400−8000=1440020000 x 1.12 = 22400. After payment: 22400 - 8000 = 14400
  2. After year 2:
    14400x1.12=16128.Afterpayment:16128−9000=712814400 x 1.12 = 16128. After payment: 16128 - 9000 = 7128
  3. After year 3:
    7128x1.12=7983.367128 x 1.12 = 7983.36

Answer: Rs 9292.48

Practice questions on Compound Interest

  1. Q1.easy

    Find the compound interest on Rs 1000 at 10% per annum for 1 year.
    1. A)Rs 100
    2. B)Rs 110
    3. C)Rs 200
    4. D)Rs 1100
    Show answer

    Answer: Rs 100

    Hint: For 1 year, CI equals SI.

  2. Q2.easy

    Find the amount when Rs 5000 is invested at 8% per annum compounded annually for 2 years.
    1. A)Rs 5800
    2. B)Rs 5832
    3. C)Rs 5400
    4. D)Rs 6000
    Show answer

    Answer: Rs 5832

    Hint: Use A = P(1 + r/100)^n with P = 5000, r = 8, n = 2.

  3. Q3.easy

    The difference between CI and SI on a sum for 2 years at 10% per annum is Rs 50. Find the sum.
    1. A)Rs 5000
    2. B)Rs 500
    3. C)Rs 50000
    4. D)Rs 2500
    Show answer

    Answer: Rs 5000

    Hint: For 2 years, CI - SI = P(r/100)^2.

  4. Q4.medium

    The population of a city increases by 5% each year. If the current population is 200000, find the population after 2 years.
    1. A)210000
    2. B)220000
    3. C)220500
    4. D)221000
    Show answer

    Answer: 220500

    Hint: Population growth uses the CI formula: P_new = P(1 + r/100)^n.

  5. Q5.medium

    A machine worth Rs 80000 depreciates at 10% per annum. Find its value after 3 years.
    1. A)Rs 56000
    2. B)Rs 58320
    3. C)Rs 54000
    4. D)Rs 60000
    Show answer

    Answer: Rs 58320

    Hint: Use the depreciation formula: V = P(1 - r/100)^n.

  6. Q6.medium

    Find the CI on Rs 16000 at 15% per annum for 2 years compounded annually.
    1. A)Rs 4800
    2. B)Rs 5160
    3. C)Rs 4960
    4. D)Rs 5000
    Show answer

    Answer: Rs 5160

    Hint: A = 16000(1.15)^2.

  7. Q7.hard

    Find the rate of interest at which Rs 4000 amounts to Rs 4410 in 2 years when interest is compounded half-yearly.
    1. A)5%
    2. B)10%
    3. C)8%
    4. D)12%
    Show answer

    Answer: 10%

    Hint: For half-yearly compounding with n = 2 years, there are 4 periods. Find the half-yearly rate first.

  8. Q8.hard

    The CI on a sum for 2 years at 10% per annum, compounded annually, is Rs 840. Find the sum.
    1. A)Rs 3000
    2. B)Rs 4000
    3. C)Rs 3500
    4. D)Rs 5000
    Show answer

    Answer: Rs 4000

    Hint: CI for 2 years at 10% = P x [(1.1)^2 - 1] = P x 0.21.

  9. Q9.hard

    A sum of money doubles itself at CI in 15 years. In how many years will it become 8 times?
    1. A)30 years
    2. B)45 years
    3. C)60 years
    4. D)40 years
    Show answer

    Answer: 45 years

    Hint: 8 = 2^3. If doubling takes 15 years, then 8x takes 3 x 15 years.

These are 9 of the 60 questions available for Compound Interest. Start practicing above to unlock visual solutions, AI coaching, and the topic leaderboard — completely free.