What is the rate of interest p.c.p.a.?

I. An amount doubles itself in 5 years on simple interest.

II. Difference between the compound interest and the simple interest earned on a certain amount in 2 years is Rs. 400.

III. Simple interest earned per annum is Rs. 2000

We know thatThe Difference between Compound Interest and Simple Interest for n years at R rate of interest is given by C.In - S.In = PR100n

Here n = 2 years, R = 20%, C.I - S.I = 56

$$\begin{gathered} 56 = P201002 \\ => P = 56 x 52 \\ => P = 56 x 25 \\ => P = Rs. 1400 \end{gathered}$$

We know Compound Interest = C.I. = P1+r100t - 1

Here P = 2680, r = 8 and t = 2

C.I. = 26801 + 81002-1= 268027252-12= 26802725+12725-1= 2680 5225×225

= (2680 x 52 x 2)/625

= 445.95

Compound Interest = Rs. 445.95

8000 × 33.1% = 2648

Given C.I = 5984, R = 20% , T = 2yrs

 C.I = P1+201002-1

5984 = 

=> P = (5995x25)/11

P = Rs. 13625

Now S.I = PTR/100

SI = (13625 x 8 x 6)/100 = Rs. 6540

Given compound interest for 3 years = Rs. 1513.2

and simple interest for 5 years = Rs. 2400

Now, we know that  C.I = P1+R100n - 1

=> 1513.2 = P1+R1003 - 1 ...........(A)

And S.I = PTR/100

=> 2400 = P5R/100 ..................(B)

By solving (A) & (B), we get

R = 5%.

Let the sum be Rs. P
P{ 1+81002- 1 } = 2828.80

It is in the form of  a2-b2 = a+ba-b

P(8/100)(2 + 8/100) = 2828.80

P = 2828.80 / (0.08)(2.08)

= 1360/0.08 = 17000

Principal + Interest = Rs. 19828.80

P = Rs. 15225, n = 9 months = 3 quarters, R = 16% p.a. per quarter.

Amount = 15225x1+41003

= (15225 x 26/25 x 26/25 x 26/25) = Rs. 17126.05

=> C.I. = 17126 - 15625 = Rs. 1901.05.

P1+20100n > 2P 

Now, (6/5 x 6/5 x 6/5 x 6/5) > 2.

So, n = 4 years.