# Aptitude - Compound Interest - Discussion

Discussion Forum : Compound Interest - General Questions (Q.No. 2)
2.
The difference between simple and compound interests compounded annually on a certain sum of money for 2 years at 4% per annum is Re. 1. The sum (in Rs.) is:
625
630
640
650
Explanation:

Let the sum be Rs. x. Then,

 C.I. = x 1 + 4 2 - x = 676 x - x = 51 x. 100 625 625

 S.I. = x x 4 x 2 = 2x . 100 25

 51x - 2x = 1 625 25

x = 625.

Discussion:
135 comments Page 1 of 14.

SICI said:   4 weeks ago
In C. I = where -x is come from? Please explain me.

Joa said:   4 weeks ago
Thanks everyone for explaining the answer.

Saudagar Rokade said:   1 month ago
Diff = PR^²/10000.

1 = P×4^²/10000,
10000 = P×16,
P = 10000/16,
P = 625.
(1)

Vanhel said:   2 months ago
SI = 8%.
CI = 8.16%.
CI - SI = 1.
8.16% - 8% = 1.
0.16% = 1.

Sum of the difference principal = 1/0.16 * 100 = 625.
(2)

P manoj said:   1 year ago
It is simply derived by using this formula => Diff =PR^2/100^2 -> It is only for 2 years difference.

Given -> Diff=1 , R =4, Tp find P?

By Formula ,
Diff = PR^2/100^2.
1 = P * 4 * 4/100 * 100.
1= P * 1/20 * 1/20.

Note : (Also for three years difference use this formula -> Diff = PR^2(300 + R)/100^3).
(5)

Naveen said:   2 years ago
1=10000*x/4 * 4.
= 625.

Kurdush said:   2 years ago
Shortcut to solve :

(100*100*Diff)/Rate * Rate.
here diff =1.
rate=4.

Substitute in above formula u get Rs.625.
(3)

Hi.

Before solving this question you have to be aware on S.I and C.I formula's.

S.I = PTR/100.

Where as AMOUNT = P (1+ R/100) ^T ====> IN C.I.

AMOUNT = P + C.I.

C.I = P (1+ R/100) ^T - P.

In the question, they give the difference between S.I AND C.I is rupee 1.

First Calculate S.I.

Let the PRINCIPAL or SUM be ==> '' P '', TIME = 2, RATE = 4%.

S.I = PTR/100 ==> P*2*4/100 ==> 2P/25.

Now C.I = P (1+R/100) - P ==> P (1+4/100) - P ==> 51P/625.
51P/625 - 2P/25 = 1.
LCM IS 625.
51P - 50P/625 = 1.
P = 625.

I hope this will be helpful.

Thank you.
(23)

Mohit said:   2 years ago
(3)

Sumit said:   3 years ago
Diff = p(R/100) ^n.

By using this formula you can directly find the amount i.e. p.

1=p(4/100) ^2.
=> p=625.
(2)