Transcript Inverse Proportion Inverse Proportion Inverse Proportion is when one quantity increases and the other decreases.

Inverse Proportion
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 :
y
Fill in the following table given x and y
are inversely proportional.
X
x
y
1
2
4
8
80 40 20 10
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
Number of
people
Time in days.
Less Time
Less people
4
2
1
2
4
8
More Time
Example : If it takes 3 men 8 hours to build a wall.
How long will it take 4 men. (Less time !!)
Men
y
x
Hours
3

8
1

3 x 8 = 24 hours
4

24 ÷ 4 = 6 hours
Example : It takes 10 men 12 months to build
a house.
How long should it take 15 men.
Men
y
x
Months
10

12
1

12 x 10 = 120
15

120 ÷ 15 = 8 months
Example : At 8 m/s a journey takes 32 minutes.
How long should it take at 10 m/s.
Speed
y
x
Time
8

32 mins
1

32 x 8 = 256 mins
10

256 ÷ 10 = 25.6 mins
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?
2-Nov-15
Created by Mr. Lafferty Maths Dept.