Direct proportion and inverse proportion

Direct proportion and inverse proportion

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2. BY: ASSOCIATE PROFESSOR NADEEM UDDIN


Direct Proportion:

If two quantities are in direct proportion as one increases, the other increases or
one decreases the other decreases.


Example-14

If 30 dozens of eggs cost Rs.300.Find the cost of 5 dozens eggs.

Solution:
Cost Dozens
300 30
x 5
x5
=
300 30
5
x = 300
30
x = Rs.50




Example-15

A car travel 81 km in 4.5 liters. How far will it goes by 20 liters of petrol.

Solution:

Km Liters
81 4.5
x 20

x 20
=
81 4.5
20
x =
4.5
x = 360 km


3. Inverse Proportion:

If increased in one quantity causes decreased in other quantity or decrease in one
quantity,causes increased in other quantity then we say that both quantities are
inversely related.


Example-16

Four pipes can fill a tank in 70 minutes. How long will it take to fill the tank by 7
pipes?

Solution:

Minutes Pipes
70 4
x 7
x4
=
70 7
4
x =
7
x = 40 minutes
 




Example-17

35 workers can build a house in 16 days. How many days will 28 workers working
at the same rate take to build the same house?

Solution:

Days workers
16 35
x 28
x 35
16 28
35
x 16
28
x 20 days
=
=
=