Aptitude - Compound Interest - Discussion

Discussion Forum : Compound Interest - General Questions (Q.No. 12)
12.
If the simple interest on a sum of money for 2 years at 5% per annum is Rs. 50, what is the compound interest on the same at the same rate and for the same time?
Rs. 51.25
Rs. 52
Rs. 54.25
Rs. 60
Answer: Option
Explanation:

Sum = Rs. 50 x 100 = Rs. 500.
2 x 5

Amount
= Rs. 500 x 1 + 5 2
100
= Rs. 500 x 21 x 21
20 20
= Rs. 551.25

C.I. = Rs. (551.25 - 500) = Rs. 51.25

Discussion:
10 comments Page 1 of 1.

HENRY said:   8 months ago
First, we will find the principal using the formula of SI which is PRT/100 = P * 5 * 2/100.
P = 500,
Now,
CI = P(1 +R/100) - 1 = 500(1 + 5/100)-1 = 51.25.

Hope it helps.
(1)

Mruganshi said:   1 year ago
SI is the same every year hence for S.I. = 5%+ 5% = 10%.
For C.I = (a + b + (a*b)/100) = (5+5(25)/100) = 10.25%.

Here sum is given for S.I;
so, 10% for 50.
then 10.25% for ?

10.25 * 50/10 = 51.25.

Appu said:   2 years ago
The difference when the time period is 2 years, where only the SI and rate of interest are given, will be;
Diff= SI*R/200.
ie, (50*5)/200= 1.25.
(1)

Khyati mehta said:   4 years ago
Given t=2 years, rate=5%, SI=50.
So, from this 50 = (P*5*2)/100
P = 500.

Now use formula of difference for 2 years.
CI -SI =p*(R/100)^2.
CI-50=500(5/100)^2.
CI = 51.25.
(2)

Sambasiva reddy said:   5 years ago
Difficult to understand.

Shruti jha said:   7 years ago
difficult to understand

Prathap reddy said:   8 years ago
Very good @Krishna.

Surya said:   8 years ago
How it comes 21?

Krishna said:   1 decade ago
USED METHOD:

here they have calculated the principal from the the formula :

sum = principal in this case.

PRT/100 = S.I; re-arrange and get the principal.

Use this principal in the C.I formula to get the amount after two years.subtracting the principal from amount gives you the compound interest.

Alternative:

Find the principal from the S.I formula.

And use the formula:

S.I -C.I = p * (r/100)^2.

This one saves time and is easier to calculate.

Satej said:   1 decade ago
What is that sum? what is the formula?

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