###
**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