Tricky Questions from Simple Interest with Solutions

simple interest

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
        T --- Time 

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 

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