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Growth multiple of a sum at annual compound interest: least years or the multiple

This type of question, asked 4 times: CDS 2 2019, CDS 2 2023, CDS 1 2025, CDS 2 2026. All 4 questions below, oldest first.

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  1. Question 1

    CDS 2 2019

    44
    What is the least number of complete years in which a sum of money put out at 40% annual compound interest will be more than trebled ?

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  2. Question 2

    CDS 2 2023

    53
    A sum of money at 20% rate of compound interest per annum becomes more than 100 times in n years. What is the least value of n ? (Use log⁡102=0.301\log_{10} 2 = 0.301, log⁡103=0.477\log_{10} 3 = 0.477)

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  3. Question 3

    CDS 1 2025

    49
    What is the least number of complete years in which a sum of money put out at 20% compound interest (compounded annually) will be more than doubled ?

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  4. Question 4

    CDS 2 2026

    28
    A sum of money at the rate of 5% per annum compounded annually becomes n times in 100 years. What is the value of n ? (Given log⁡102=0.301\log_{10} 2 = 0.301, log⁡103=0.477\log_{10} 3 = 0.477 and log⁡107=0.845\log_{10} 7 = 0.845)

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