Compound Interest


  1. If the difference between the compound interest and simple interest on a sum of money at 5% pa for 2 yr is ₹ 16, then find the simple interest ?









  1. View Hint View Answer Discuss in Forum

    Given, CI - SI = 16, R = 5%, n = 2 yr and SI = ?
    According to the formula,
    CI - SI = (SI x R)/200
    ⇒ 16 = (SI x 5)/200

    Correct Option: D

    Given, CI - SI = 16, R = 5%, n = 2 yr and SI = ?
    According to the formula,
    CI - SI = (SI x R)/200
    ⇒ 16 = (SI x 5)/200
    ⇒ 16 = SI/40
    ∴ SI = ₹ 640


  1. A sum, at the compound rate of interest, becomes 21/2 times in 6 yr. The same sum becomes what times in 18 yr ?









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    If sum is P, then P becomes 5P/2 in 6 yr.
    5P/2 becomes 25P/4 in 12 yr.
    25P/4 becomes 125P/8 in 18 yr.

    Correct Option: C

    If sum is P, then P becomes 5P/2 in 6 yr.
    5P/2 becomes 25P/4 in 12 yr.
    25P/4 becomes 125P/8 in 18 yr.
    The sum becomes 125/8 times in 18 yr.



  1. The cost price of an LCD TV set is ₹ 100000. If its price value depreciates at the rate of 10% pa. then what will be the price at the end of 3 yr?









  1. View Hint View Answer Discuss in Forum

    Given P = ₹ 100000, R = 10%, n = 3 yr
    According to the formula,
    Price of LCD TV set after 3 yr. = P(1 - R/100)n
    = 100000 (1 - 10/100)3

    Correct Option: D

    Given P = ₹ 100000, R = 10%, n = 3 yr
    According to the formula,
    Price of LCD TV set after 3 yr. = P(1 - R/100)n
    = 100000 (1 - 10/100)3
    = 100000(90/100)3
    = 100000 x (9/10) x (9/10) x (9/10)
    = ₹ 72900


  1. A sum of ₹ 400 amounts to ₹ 441 in 2 yr. What will be its amount, if the rate of interest is increased by 5% ?









  1. View Hint View Answer Discuss in Forum

    According to the given condition.
    441 = 400 (1 + R/100)2
    ⇒ 441/400 = (1 + R/100)2
    ⇒ (21/20)2 = (1 + R/100)2
    ⇒ 21/20 = 1 + R/100
    ⇒ (21/20) - 1 = R/100
    ⇒ R/100 = 1/20
    ∴ R = 5%
    ∴ new rate = 5 + 5 = 10%
    ∴ Amount = 400 (1 + 10/100)2

    Correct Option: A

    According to the given condition.
    441 = 400 (1 + R/100)2
    ⇒ 441/400 = (1 + R/100)2
    ⇒ (21/20)2 = (1 + R/100)2
    ⇒ 21/20 = 1 + R/100
    ⇒ (21/20) - 1 = R/100
    ⇒ R/100 = 1/20
    ∴ R = 5%
    ∴ new rate = 5 + 5 = 10%
    ∴ Amount = 400 (1 + 10/100)2
    = 400 x (11/10) x (11/10)
    = ₹ 484



  1. The population of a city increases at the rate of 5% pa. If the present population of the city is 185220, then what was its population 3 yr ago?









  1. View Hint View Answer Discuss in Forum

    Given, P = 185220 R = 5% (increases) and n = 3 yr
    According to the formula,
    Population n yr ago = P/(1 + R/100)n
    = 185220/(1 + 5/100)3

    Correct Option: C

    Given, P = 185220 R = 5% (increases) and n = 3 yr
    According to the formula,
    Population n yr ago = P/(1 + R/100)n
    = 185220/(1 + 5/100)3
    = 185220/[(21/20) x (21/20) x (21/20)]
    = [185220 x 20 x 20 x 20] / [21 x 21 x 21]
    = 20 x 20 x 20 x 20
    = 160000