Simple Interest :
If interest is calculated on the Original principal for a period of time , then it is called simple interest.
Simple Interest (S.I) = (P×T×R)/100
Here P --- Principal
R --- Rate
Different Conditions :
For Half-yearly :
Rate become = Rate/2
Time become = Time×2
For Quarterly :
Rate become = Rate/4
Time become = Time×4
For Monthly :
Rate become = Rate/12
Time become = Time×12
* If a sum of money becomes N times in T years at simple interest , then Rate = 100(N-1)/T
Ques 1.
Find the simple interest on 300 for 5 years at 5% per annum ?
Solution :
Consider 300 as 100%
Rate × Time = 5×5 = 25%
300 ------- 100%
? ------- 25%
Simple Interest = 75
Ques 2.
In what time , 1000 will become 1250 when the annual rate of interest is 20% ?
Solution:
Simple Interest = 1250-1000 = 250
T = ?
Rate = 20
Rate * Time = 20* T
1000 ----- 100%
250 ----- 20*T
T = 5/4 years
Ques 3.
A sum at simple interest of 4% per annum amounts to 3120 in 5 years . Find the principal ?
Solution :
Rate × Time = 5×4 = 20
Amount = Principal + Rate×Time = 100%+20% = 120%
120% ------ 3120
100% ------ ?
Principal = 2600
Ques 4.
Charan takes 4000 from Ravi for 2 years at the rate of 10% half-yearly interest . What amount will be paid by Charan to Ravi after end of 2 years ?
Solution :
Here Interest is calculated half-yearly
So , Rate = 10/2 = 5%
Time = 2*2= 4
Rate × Time = 5×4 = 20%
Principal = 4000 = 100%
Amount = ? = 100+20=120%
120% ------ ?
100% ------ 4000
Amount = 4800
Ques 5.
A sum of money becomes 5 times in 20 years at Simple Interest . Find the rate of interest ?
Solution :
Rate = (N-1)100/T
==> (5-1)100/20 = 20%
Ques 6.
A sum becomes three times in 5 years at a certain rate of interest . Find the time in which the same amount will be 11 times at the same rate of interest ?
Solution :
SI = 3P-P=2P
SI = P×T×R/100
==>2P = P ×5×R/100
==> R = 40%
S.I = 11P-P = 10P
==> 10P = P×40×T/100
==> T = 25 years
