1. Simple interest Time in Month and Days

2. Recap on simple interest
Amount = Principal + Interest
Where n is in years

3. Some example where period (n) is not in years
1) Period=14 months. In a year there are 12 months , so period as a fraction of year is
(after simplifying)
2) Period=200 days. In a year there are 365 days, so period as a fraction of year is
(after simplifying)
3) Period from 4th Oct 2017 to 11th Dec 2017.
We need to find the number of days between the given dates
Oct=31 days – 3 days (except days from Oct 1 to Oct 3 ) =28 days
Nov=30 days (whole month) and Dec = 10 days (from Ist to 10th Dec)
Total days = = 68 days.
So period as fraction of years is

4. Example 1: Find the simple interest due on Rs
Example 1: Find the simple interest due on Rs. 3,750 for 73 days at 5 % per annum. Solution: Given: p= 3750 , r= 5 n= To find : Simple interest
Ans: I = Rs. 375

5. Example 2: Lokesh invested Rs 2,400 in a bank that pays an interest of 7 % per annum. He
withdraws the amount after 2 years and 5 months. Find the interest, he receives.
Solution
Given: Principal(P)=2400 , Rate(r)=7% per year , Period(n)=2 year 5 months.
To find : Simple Interest(I)
Period(n) is not completely in year so lets convert it to year
n = 2 year 5 months
Convert month part as fraction of year
Ans: Interest (I) = Rs 406

6. Example 3: Find the S.I and amount on Rs 12,000 from May 21st 1999 to
August 2nd at 9 % per annum.
Solution: Given:- P = Rs 12000, Rate 9% per annum
Period from May 21st 1999 to August 2nd 1999
To find : Simple Interest(I)
We need to find the number of days between the given dates
May 21st 1999 to August 2nd 1999
May=31 days – 20 days =11 days (except days from May 1 to May 20 )
June=30 days (whole month)
July=31 days (whole month)
August = 1 day (1st Aug )
Total days = = 73 days.
So period as fraction of years is

7. Ans : Simple interest = Rs 216
2 4
I = 2 4 x 9
I = 216
Ans : Simple interest = Rs 216

8. Try these
1. Find S.I. and amount on Rs 3,600 at 15% p.a. for 3 years and 9
months.
2. Find the simple interest on Rs.7300 for 180 days at 10 % per year.