 # S.I. & C.I. (22)

1. The simple interest on a certain sum for 8 months at 4% per annum is Rs. 129 less than the simple interest on the same sum for 15 months at 5% per annum. The sum is:
1. Rs. 2580
2. Rs. 2400
3. Rs. 2529
4. Rs. 3600
5. None of these

Explanation :-

Let the sum be Rs. x
Given That  [(x*5*15)/(100*12)] – [(x*4*8)/(100*12)] = 129
75x – 32x = 129 (100*12)
x = (120*1200) / 43
x = Rs. 3600

2. A person deposited Rs. 400 for 2 years, Rs. 550 for 4 years and Rs. 1,200 for 6 years. He received the total simple interest of Rs. 1,020. The rate of interest per annum is ?
1. 10%
2.  5%
3. 15%
4. 20%
5. None of these

Explanation :-

Let Rate of interest be R%
SI(1) = (400*2*R)/100,    SI(2) = (550*4*R)/100,   SI(3) = (400*6*R)/100
Total SI = SI(1) + SI(2) + SI(3) = 1020
[(400*2*R)/100] + [(550*4*R)/100] + [(400*6*R)/100] 8R + 22R +72R = 1020
102R = 1020
R = 10%

3. A sum of money becomes 7/6 of itself in 3 years at a certain rate of simple interest. The rate per annum is?
1. 5 5/9%
2. 6 5/9%
3. 18%
4. 25%
5. None of these

Explanation :-

Let Principal be P &  Rate be R%
Amount (A) = (7/6)P
Therefore, SI = [(7/6)P] – P = P/6
SI =(PRT)/100
P/6 = (P*R*3)/100
R= 50/9  =  (5+ 5/9 )%

4. At what rate per cent per annum will the simple interest on a sum of money be 2/5 of the amount in 10 years?
1. 4
2. 6
3 5 2/3
4. 6 2/3
5. None of these

Explanation :-

Let the Sum be  Rs.x and rate = R%
(2/5)x = (x*R*10)/100
R = 200/(5*10)
R = 4%

5. Simple interest on a certain sum for 6 years is 9/25 of the sum. The rate of interest is ?
1. 6%
2. 6 1/2%
3. 8%
4. 8 1/2%
5. None of these