Surprise Test

Q: If the difference between the compound interest and simple interest on a certain sum of money for 2 years at 25/2 per annum is 150 rs.the sum is:

Solution

r=12.5%

Diff=[P(1+12.5/100)^n-P] - [P*12.5/100*n

- P ] = 150

[P(1+0.125)^2-P]-[P*0.125*2-P]

=150

[1.125^2*P-P]-[0.25P-P]=150

P[1.265625-1]-[-0.75P]=150

P*(0.265625+0.75)=150

P=150/1.015625

=147.69

Q: If the amount is 9/4 times the sum after 2 years at compound interest. find the rate

Solution

Here is your answer

Let Sum be X then A =9X/4. 
T = 2 years. R = ?
ATQ
9X/4= X(1+R/100)*2 
(3/2)*2= (1+R/100)*2
3/2 = 1+ R/100
R/100 =3/2 - 1
R =1/2(100)
R = 50%

Q: The time in which Rs 1800 amounts to Rs 2178 at 10% per annum,compounded annually is ?

Solution

2178 = 1800(1+10/100)^n (The formula is P(1+r/100)^n) 
2178/1800 = (1+10/100)^n
121/100 = (11/10)^n
(11/10)^2 = (11/10)^n
n = 2.

Q: The compound interest on a certain sum at 5% p.a. for 2 year is 328. The simple interest on that sum at the same rate and for the same period will be

Solution