1. Inverse Proportion X 1 2 4 8 y 80 40 20 10 Inverse Proportion
Inverse Proportion is when one quantity increases
and the other decreases. The two quantities are said
to be INVERSELY Proportional
or (INDIRECTLY Proportional) to each other.
Example : Fill in the following table given x and y
are inversely proportional. y x X 1 2 4 8 y 80 40 20 10

2. More people Less people Number of people 4 2 1 Time in days. 2 4 8
It takes one person 8 days to complete a job. How many days will it take 2 people? 4 people? Why do you know this?
More people
Less people
Number of people 4 2 1
Time in days. 2 4 8
More Time
Less Time

3. 3  8 4  24 ÷ 4 = 6 hours Men Hours y 1  3 x 8 = 24 hours x
Example : If it takes 3 men 8 hours to build a wall.
How long will it take 4 men. (Less time !!)
Men Hours
3  8 y x
1  3 x 8 = 24 hours
4  24 ÷ 4 = 6 hours

4. Example : It takes 10 men 12 months to build a house.
How long should it take 15 men.
Men Months y x
10  12
1  12 x 10 = 120
15  120 ÷ 15 = 8 months

5. Example : At 8 m/s a journey takes 32 minutes.
How long should it take at 10 m/s.
Speed Time
8  32 mins y x
1  32 x 8 = 256 mins
10  256 ÷ 10 = 25.6 mins

6. Created by Mr. Lafferty Maths Dept.
YOUR TURN…
0. If a school kitchen has enough food for 234 pupils for 37 days, how long will the same food last 73 pupils ?
1.   If 32 men can reap a field in 15 days, in how many days can 20 men reap the same field?  2.   12 men can dig a pond in 8 days. How many men can dig it in 6 days?  3.   A hostel has enough food for 125 students for 16 days. How long will the food last if75 more students join them?  4.   A fort had enough food for 80 soldiers for 60 days. How long would the food last if 20 more soldiers join after 15 days? 
14-Apr-17
Created by Mr. Lafferty Maths Dept.