Q.To what amount will ₹12000 accumulate in 12 years if invested at an effective rate of 5%?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Compound Interest
Compound Annual Growth Rate (CAGR)
The Intuition First
Imagine you put ₹100 into a business. After one year, it grows to ₹120. After two years, it becomes ₹150. After three years, it's ₹200.
If someone asks, "What was the average yearly growth rate?", you might be tempted to say: "Year 1 grew 20%, Year 2 grew 25%, Year 3 grew 33.3% — so average is about 26%." But that's misleading. Why? Because each year's growth compounds on the previous year's base. You can't just average percentages that act on different starting amounts.
CAGR solves this problem. It answers: "If this investment had grown at a steady, constant rate every year, what would that rate be?" It smooths out the bumps and gives you one number that tells you the true annualised return.
CAGR is not the actual return in any single year. It's the geometric average — the rate that, if applied every year, would take you from the start value to the end value.
The Precise Statement
CAGR is the mean annual growth rate of an investment over a specified period longer than one year. It represents one of the most accurate ways to calculate and determine returns for anything that can rise or fall in value over time.
CAGR=(Beginning ValueEnding Value)n1−1
Where:
- Ending Value = final value of the investment
- Beginning Value = initial value of the investment
- n = number of years
Applying It to Our Example
Beginning Value = ₹100, Ending Value = ₹200, n = 3 years.
CAGR=(100200)31−1=(2)0.333−1≈1.26−1=0.26=26%
So the CAGR is 26%. Notice this is lower than the simple average of 26.1% we calculated earlier — that's because CAGR correctly accounts for the compounding effect.
A common mistake is to use the arithmetic mean of yearly returns. For example, if an investment goes up 50% one year and down 50% the next, the arithmetic mean is 0%, but you've actually lost money (₹100 → ₹150 → ₹75). CAGR correctly gives -13.4%.
Why CAGR Matters in Exams
In Indian competitive exams (CAT, GMAT, banking, SSC, UPSC), CAGR appears in:
- Data Interpretation: Tables showing company revenues or GDP over years — you'll need to compute CAGR quickly.
- Quantitative Aptitude: Direct formula-based questions.
- Finance/Investment: Comparing mutual fund or stock returns. …
Concept: Compound Interest — the amount grows as A=P(1+i)n, where i is the effective rate per period and n is the number of periods.
Step 1: Identify the values.
Principal P=12000, effective rate i=5%=0.05, time n=12 years.
Step 2: Apply the compound interest formula.
A=12000×(1+0.05)12
Step 3: Compute (1.05)12. …
The key idea is that compound interest grows money exponentially, not linearly. Using the formula A=P(1+i)n, ₹12000 at 5% effective annual rate for 12 years accumulates to approximately ₹21,550.
Compound interest means that each year, the interest earned is added to the principal, and the next year’s interest is calculated on this larger amount. This is why it’s called “interest on interest.” The effective rate of 5% means that after one year, ₹100 becomes ₹105 — no compounding within the year, just once per year.
The formula is straightforward:
A=P(1+i)n
where A is the accumulated amount, P is the principal, i is the effective interest rate per period (as a decimal), and n is the number of periods.
Here, P=12000, i=0.05, and n=12.
-
Set up the calculation.
We need A=12000×(1.05)12.
-
Compute (1.05)12.
You can do this step by step, but it’s faster to use a calculator or logarithms. Let’s break it down for understanding:
- (1.05)2=1.1025
- (1.05)4=(1.1025)2=1.21550625
- (1.05)8=(1.21550625)2≈1.477455
- Then (1.05)12=(1.05)8×(1.05)4≈1.477455×1.215506≈1.795856
More precisely, using a calculator: (1.05)12≈1.795856326.
-
Multiply by the principal.
A=12000×1.795856326≈21550.2759
- Round to the nearest rupee. …
Showing the 12 most recent of 39 on this concept.
- CA Foundation 2026Set jan-20261 markMCQQ.If an amount is compounded annually so that it tripled itself in 4 years, then the annual rate of interest is (Given that 31/4=1.316) (A) 13.6% (B) 31.1% (C) 31.6% (D) 11.3%
›Reveal solutionSolution
(1+r)4=3⇒1+r=31/4=1.316⇒r=31.6%.
Step 1 — set up the compound-growth equation
Tripling in 4 years: P(1+r)4=3P, so
(1+r)4=3.
Step 2 — take the fourth root
1+r=31/4=1.316.
Step 3 — extract the rate
r=1.316−1=0.316=31.6% per annum.
Watch outRemember to subtract 1 after taking the root. 31/4=1.316 is the growth factor, not the rate — reading 13.6% (option A) by misplacing the digits, or forgetting the −1, are the built-in traps here. …
- CA Foundation 2026Set jan-20261 markMCQQ.Bank B provides loans at 15% per annum compound interest. If Mr. XYZ borrowed ₹ 3,200 for 2 years from Bank B, then how much interest must Mr. XYZ pay to his bank? (A) ₹ 400 (B) ₹ 960 (C) ₹ 4,232 (D) ₹ 1,032
›Reveal solutionSolution
A=3200(1.15)2=₹4,232; interest =4232−3200=₹1,032.
Step 1 — compound amount
A=P(1+r)n=3200(1.15)2.
Since (1.15)2=1.3225:
A=3200×1.3225=₹4,232.
Step 2 — interest = amount − principal
CI=4232−3200=₹1,032.
Watch outOption (C) ₹4,232 is the total amount payable, not the interest. The question asks only for the interest, so you must subtract the principal — stopping at the amount is the most common trap on this question. …
- CA Foundation 2026Set jan-20261 markMCQQ.If ₹ 80,000 grows to ₹ x in 3 years at compound interest compounded annually at 8% rate of interest per annum, then the value of x is: (A) ₹1,00,776.96 (B) ₹1,02,985.98 (C) ₹1,03,680.64 (D) ₹99,850.50
›Reveal solutionSolution
A=P(1+i)n=80000×(1.08)3=₹1,00,776.96.
Step 1 — Formula
For annual compounding, the maturity value is
A=P(1+i)n.
Step 2 — Substitute
With P=₹80,000, i=8%=0.08, n=3:
A=80000×(1.08)3.
Step 3 — Evaluate the factor
(1.08)3=1.259712.
Step 4 — Compute
A=80000×1.259712=₹1,00,776.96. …
- CA Foundation 2026Set jan-20261 markMCQQ.The value of compound interest (in nearest ₹) if ₹30,00,000 is deposited in a bank for 1 year at the rate of 16% per annum compounded quarterly is: (A) 5,07,575 (B) 5,78,360 (C) 5,09,576 (D) 5,72,540
›Reveal solutionSolution
A=30,00,000×(1.04)4=₹35,09,575.68, so CI=A−P≈₹5,09,576.
Step 1 — Set per-period rate and periods
Nominal 16% compounded quarterly: rate per quarter i=16%/4=4%=0.04; number of quarters in 1 year n=4.
Step 2 — Amount
A=P(1+i)n=30,00,000×(1.04)4.
(1.04)4=1.16985856,
so
A=30,00,000×1.16985856=₹35,09,575.68.
Step 3 — Compound interest
CI=A−P=35,09,575.68−30,00,000=₹5,09,575.68≈₹5,09,576. …
- CA Foundation 2026Set jan-20261 markMCQQ.A sum of money lent at compound interest for 2 years at 20% pa would fetch ₹ 482/- more if the interest was payable half yearly then if it was payable annually. What is the value of sum deposited? (A) ₹ 10,000 (B) ₹ 15,000 (C) ₹ 17,500 (D) ₹ 20,000
›Reveal solutionSolution
Half-yearly CI =0.4641P, annual CI =0.44P; difference 0.0241P=482⇒P=₹20,000.
Step 1 — Annual compounding
Rate 20% p.a., 2 years:
A=P(1.20)2=1.44P,CIannual=0.44P.
Step 2 — Half-yearly compounding
Rate per half-year =10%, periods =4:
A=P(1.10)4=1.4641P,CIhalf=0.4641P.
Step 3 — Set up the difference
CIhalf−CIannual=(0.4641−0.44)P=0.0241P=482.
Step 4 — Solve
P=0.0241482=₹20,000. …
- CA Foundation 2026Set may-20261 markMCQQ.If the difference between the annually compounded interest and simple interest on a certain sum of money at 8% per annum for 3 years is ₹ 788. Then the principle amount is ______. (A) ₹ 39,175 (B) ₹ 39,475 (C) ₹ 39,975 (D) ₹ 40,475
›Reveal solutionSolution
Use the 3-year difference formula CI−SI=P[(1+r)3−1−3r]; solving 788=P(0.019712) gives P≈₹39,975.
Step 1 — Write the difference formula
For 3 years the difference between compound interest and simple interest is:
CI−SI=P[(1+r)3−1−3r]
where r is the rate per rupee.
Step 2 — Substitute r=0.08
(1.08)3=1.259712
(1+r)3−1−3r=1.259712−1−0.24=0.019712
Step 3 — Solve for the principal
788=P×0.019712
P=0.019712788≈₹39,975 …
- CA Foundation 2026Set may-20261 markMCQQ.Raju deposit ₹ 20,000 in a nationalized bank for 3 years at an annual interest rate of 8%, with the interest compounded every quarter. Find out how much interest Raju earns in the first year and the second year. (A) ₹ 1,632 & ₹ 1,712 (B) ₹ 1,684 & ₹ 1,738 (C) ₹ 1,648 & ₹ 1,784 (D) ₹ 1,696 & ₹ 1,746
›Reveal solutionSolution
With 2% per quarter the annual growth factor is (1.02)4−1≈0.08243; applying it year by year gives interest of ₹1,648 (year 1) and ₹1,784 (year 2).
Step 1 — Find the quarterly rate and annual factor
Nominal 8% p.a. compounded quarterly ⇒ 2% per quarter. In one year (4 quarters) the balance grows by:
(1.02)4=1.082432 ⇒ annual interest factor=0.082432
Step 2 — First year's interest
I1=20,000×0.082432≈₹1,648.6≈₹1,648
Balance at end of year 1 =20,000+1,648.6=₹21,648.6.
Step 3 — Second year's interest
The same factor now acts on the larger balance:
I2=21,648.6×0.082432≈₹1,784.5≈₹1,784 …
- CA Foundation 2026Set may-20261 markMCQQ.The compound interest for ₹ 15,000 at 20% per annum for 2 years compounded semi-annually is ________. (A) ₹ 9,661.50 (B) ₹ 6,961.50 (C) ₹ 9,691.50 (D) ₹ 6,696.15
›Reveal solutionSolution
Half-year rate 10%, 4 periods: A=15000(1.1)4=21961.50, CI =A−P=6961.50.
Step 1 — Adjust rate and periods for semi-annual compounding
Rate per period =220%=10%; number of periods =2×2=4.
Step 2 — Compound amount
A=P(1+2i)2n=15000(1.10)4
=15000×1.4641=₹21,961.50
Step 3 — Compound interest
CI=A−P=21961.50−15000=₹6,961.50
Why the other options are wrong
- (A) ₹9,661.50 and (C) ₹9,691.50 mistakenly report an amount-like figure or use a wrong power.
- (D) ₹6,696.15 is a digit-transposed distractor of the correct 6,961.50. …
- CA Foundation 2026Set may-20261 markMCQQ.In how many years will ₹ 50,000 become ₹ 75,000 at 8% per annum compound interest? (Given log(1.5)= 0.1761 and log(1.08) = 0.0334) (A) 4.8 years (B) 5.1 years (C) 5.3 years (D) 5.6 years
›Reveal solutionSolution
Set (1.08)n=5000075000=1.5 and take logarithms: n=log1.08log1.5=0.03340.1761≈5.3 years.
Step 1 — Compound-interest growth equation
A=P(1+i)n
Step 2 — Form the ratio
P=50000, A=75000, i=8%=0.08:
(1.08)n=5000075000=1.5
Step 3 — Take logarithms and solve
nlog(1.08)=log(1.5)⇒n=log1.08log1.5=0.03340.1761
n=5.27≈5.3 years
Why the other options are wrong: (A) 4.8, (B) 5.1 and (D) 5.6 do not equal 0.1761/0.0334; they come from mis-dividing or rounding early. …
- CA Foundation 2025Set jan-20251 markMCQQ.Anil deposited a certain amount in a bank at the rate of 10% per annum compounded semi-annually. At the end of one year Anil received a sum of ₹ 13,230. Then the sum deposited in the bank is (A) ₹ 13,000 (B) ₹ 1,200 (C) ₹ 12,000 (D) ₹ 5,000
›Reveal solutionSolution
Semi-annual: i=5%, n=2; P(1.05)2=13230⇒P=₹12,000.
Step 1 — Adjust rate and periods for semi-annual compounding
Nominal 10% p.a. compounded semi-annually → rate per half-year =5%, number of half-years in 1 year =2.
Step 2 — Apply the compound amount formula
A=P(1+i)n=P(1.05)2=1.1025P
Step 3 — Solve for the deposit
1.1025P=13230⇒P=1.102513230=12000
Why the other options are wrong: (A) ₹13,000 is close to the maturity value, not the deposit; (B) ₹1,200 and (D) ₹5,000 are off by an order of magnitude / do not compound to ₹13,230. …
- CA Foundation 2025Set jan-20251 markMCQQ.What is the present value of ₹ 8,000 to be required after 10 years if the interest rate be 6% ? (Given that (1.06)10=1.7908) (A) ₹ 6,499.87 (B) ₹ 4,467.28 (C) ₹ 5,867.32 (D) ₹ 1,790.86
›Reveal solutionSolution
PV=(1.06)108000=1.79088000=₹4,467.28.
Step 1 — Identify a single-sum present value
A single amount FV=₹8,000 is due after n=10 years; discount it at i=6%=0.06.
Step 2 — Apply the discounting formula
PV=(1+i)nFV=(1.06)108000
Step 3 — Substitute and compute
PV=1.79088000=4467.28
Why the other options are wrong: (A) ₹6,499.87 and (C) ₹5,867.32 under-discount the amount; (D) ₹1,790.86 is essentially the discount FACTOR ×1000, not the present value. …
- CA Foundation 2025Set jan-20251 markMCQQ.A certain amount is invested in a bank. What annual rate of interest compounded annually becomes 8 times of this investment in 5 years ? (Given that 81/5=1.515716) (A) 51.57% (B) 5.15% (C) 15.15% (D) 1.51%
›Reveal solutionSolution
If money becomes 8 times in 5 years, then (1+r)5=8⇒r=81/5−1=51.57%.
Step 1 — Set up the compound-interest equation
Under annual compounding the amount after n years is A=P(1+r)n. Here the amount becomes 8 times the principal in 5 years, so A=8P and n=5.
8P=P(1+r)5⇒(1+r)5=8
Step 2 — Take the 5th root
1+r=81/5=1.515716
r=1.515716−1=0.515716
Step 3 — Convert to a percentage
r=0.515716×100≈51.57%
Why the other options are wrong: (B) 5.15% and (D) 1.51% are decimal-shift errors on the correct digits; (C) 15.15% wrongly reads 81/5 as giving 0.1515. …
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