Finding Percentage Increase and Decrease
There are 10 children in each group below.
2 more children join Group A. The number of children in Group A increases by 2.


There are now 20% more children in Group A than before. 
3 children from Group B leave the group. The number of children in Group B decreases by 3.


There are now 30% fewer children in Group B than before. 
Percentage increase  =  amount increased initial quantity  × 100% 
Percentage decrease  =  amount decreased initial quantity  × 100% 
Word Problem 1
Lisa's salary was raised from $4000 to $4800 per month. What was the percentage increase in her monthly salary?
Percentage increase = $800
$4000× 100% = 20%
The percentage increase in her monthly salary was 20%.
Word Problem 2
The price of a chair was reduced from $270 to $189 in a sale. Find the percentage discount on the chair.
Decrease in price = $270 − $189 = $81
Percentage decrease = $81
$270× 100% = 30%
The percentage discount on the chair was 30%.
Word Problem 3
Joey had a leaky water bottle that leaked 15 ml of water every 10 minutes. What was the percentage decrease in the water in the bottle 1 hour after the bottle was filled up to 450 ml?
After 1 hour 90 ml of water had leaked from the bottle.
10 minutes 15 ml 1 minute 15
10ml 60 minutes 15
10ml × 60 = 90 ml
Percentage decrease = 90
450× 100% = 20%
The percentage decrease in the water after 1 hour was 20%.
Word Problem 4
Due to some roadworks on the usual route from home to school, Peggy has to take another route to school which is 7% longer. This increase in distance is 126 m. What is the length of the new route?
7% 126 m 1% 126
7m = 18 m 107% 18 m × 107 = 1926 m
The length of the new route is 1926 m.
Word Problem 5
Sue bought a piece of cloth 140 cm long. After washing it, the cloth shrank by 4% along its length. What is the length of the cloth now?
100% − 4% = 96% 96% of 140 cm = 96
100× 140 cm = 134.4 cm
The length of the cloth is 134.4 cm now.