PERCENTAGE INCREASE AND DECREASE

Example 1 :

Increase 20 by 50%

Solution :

Original quantity = 20

Should be increased by 50%.

Original quantity can be considered as 100%.

Then the new quantity = (100 + 50)% of the old quantity

= 150% of 20

= 1.50 (20)

= 30

Example 2 :

Increase 32 by 75%

Solution :

Original quantity = 32

Should be increased by 75%.

Original quantity can be considered as 100%.

Then the new quantity = (100 + 75)% of the old quantity

= 175% of 32

= 1.75 (32)

= 52.5

Example 3 :

Decrease 55 by 40%

Solution :

Original quantity = 55

Should be decreased by 40%.

Original quantity can be considered as 100%.

Then the new quantity = (100 - 40)% of the old quantity

= 60% of 55

= 0.60 (55)

= 33

Example 4 :

Decrease 6 kg by 5%

Solution :

Original quantity = 6

Should be decreased by 5%.

Original quantity can be considered as 100%.

Then the new quantity = (100 - 5)% of the old quantity

= 95% of 6

= 0.95 (6)

= 5.7

Example 5 :

Increase 670 by 1.2%

Solution :

Original quantity = 670

Should be increased by 1.2%.

Original quantity can be considered as 100%.

Then the new quantity = (100 - 1.2)% of the old quantity

= 98.8% of 6

= 0.988 (6)

= 5.928

Example 6 :

When a tennis ball is dropped, it bounces and then rises. The ball rises to 80% of the height from which it is dropped. The ball is dropped from a height of 4 meters.

(a) Calculate the height of the rise after the first bounce.

(b) Calculate the height of the rise after the second bounce.

Solution :

(a) Height of the ball when it is dropped = 4 meters

The ball rises 80% of the original height.

So, 180% of the ball's height = 1.80(4)

= 7.2 meter

Now the height of the ball is 7.2 meter.

(b) Again it will raise 80% of the original height.

So, 180% of 7.2 :

= 1.80 (7.2)

= 12.96