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Question

In how many years will a sum of ₹16,000 at 10% per annum compounded semi-annually become ₹18,522?

This question was previously asked in
RRB ALP 2025 CBT 2 Wiremen Question Paper (28-Jul-2026) (Shift 2)
The correct answer is

1.5 years

To determine in how many years a sum of ₹16,000 will become ₹18,522 at 10% per annum compounded semi-annually, we use the compound interest formula:

\(A = P \left(1 + \frac{r}{n}\right)^{nt}\)

where:

  • \(A\) is the amount after time \(t\).
  • \(P\) is the principal amount (₹16,000).
  • \(r\) is the annual interest rate (10% or 0.10).
  • \(n\) is the number of times the interest is compounded per year (2 times for semi-annual).
  • \(t\) is the time in years.

Given \(A = 18522, P = 16000, r = 0.10,\) and \(n = 2\), we need to find \(t\).

Plug in the values into the formula:

\(18522 = 16000 \left(1 + \frac{0.10}{2}\right)^{2t}\)

Calculate \(\left(1 + \frac{0.10}{2}\right)\):

\(\left(1 + \frac{0.10}{2}\right) = 1.05\)

Rewrite the equation:

\(18522 = 16000 \times (1.05)^{2t}\)

Divide both sides by 16000:

\(\frac{18522}{16000} = (1.05)^{2t}\)

Simplify the fraction:

\(1.157625 = (1.05)^{2t}\)

To solve for \(t\), take the logarithm of both sides:

\(\log(1.157625) = 2t \cdot \log(1.05)\)

Calculate the logarithms (using a calculator):

  • \(\log(1.157625) \approx 0.063198\)
  • \(\log(1.05) \approx 0.021189\)

Substitute these values into the equation:

\(0.063198 = 2t \cdot 0.021189\)

Solve for \(t\):

\(2t = \frac{0.063198}{0.021189}\)

\(2t \approx 2.982\)

\(t \approx \frac{2.982}{2} = 1.491\)

Round to the nearest half year, we find \(t = 1.5\) years.

Thus, the correct answer is 1.5 years.

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Similar Questions

  1. A sum of Rs. 10000 was deposited in a bank that offer 20% annual compound interest. What will the amount be in the bank after 2 year?

  2. A sum of money invested at a compound interest amounts to 800 in 2 year and 840 in 3 year. The rate of interest is:

  3. Shams invested Rs. 4000 at 10% per annum compound interest. After n years, Shams received Rs. 1324 more, Find the value of n.

  4. How much will a sum of Rs 2500, invested at compound interest, amount to in 1 year at 4% interest rate, interest compounded half-yearly?

  5. If sum of Rs. 1000 amount to Rs. 1331 in 3 years, compounded annually. Then, find rate of interest per annum?

  6. A sum of Rs. 10,000 amounts to Rs. 11, 449 in 2 years, when the interest is compounded annually. The interest rate percent per annum is:

  7. What is the difference between the compound interests on a sum Rs. 10,000 for 1 year at 10% per annum, when compounded yearly and half-yearly?

  8. If the compound interest received on a certain amount in the first year is Rs. 1,440. What will be the compound interest for the second year on the same principal at a 10% rate of interest?

  9. Find the compound interest on ₹5,70,000 for 1.5 years at 10% per annum compounded half-yearly.

  10. Consider the given question and decide which of the following statements is sufficient to answer the question.

    X took a loan from Y on compound interest. Find the rate per annum?

    Statements:

    1. After 3 years, X paid Rs. 500 as interest.

    2. After 3 years, X paid Rs. 1,500 to clear his loan with Y.


Important Questions from Compound Interest

  1. A person borrowed Rs. 10000 on compound interest at the rate of 40 percent per annum. If the interest is compounded half yearly, then what will be the amount to be paid after 1.5 years?

  2. The difference between the compound interest (compounding annually) and the simple interest on a sum of money at the rate of 40 per cent per annum for 2 years is Rs. 2400. What is the amount?

  3. In how many years will a sum of Rs.1875 amount to Rs.2187 at 8 percent p.a. compound interest?

  4. A sum of money has increased by 45% in 9 years at simple interest. What will be the compound interest of Rs. 12,000 after 3 years at the same rate?

  5. At a certain rate of compound interest a certain sum amounts to Rs. 64800 in 4 years and Rs. 93312 in 6 years. What is the compound interest earned in fifth year?

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