It is useful to memorise the percentage equivalents of common fractions such as 1/2, 1/4, etc.
Whether with fractions or percentages, it is important to identify the base quantity. For example, when there's an increase in someone's salary, the base is always his previous salary.
Example1:
Mr Tan's salary is increased by 15%. If his old salary is $1500, what is his new salary?
Old salary à 100% ($1500)
Increase % à 15%
New salary à 115%
1% of salary à $1500 ÷ 100 = $15
New salary =
115 × $15
= $1725 Ans: $1725
Example2:
Ms Lee's salary is increased by 5%. If her new salary is $1890, what was her old salary?
Old salary à 100%
Increase % à 5%
New salary à 105% ($1890)
1% of salary à $1890 ÷ 105 = $18
Old salary = 100% × $18
= $1800 Ans: $1800
Example3:
Bala had $200. He spent 40% of the money on a toy. How much money had he left?
Original amount à 100% ($250)
Spent à 40%
Left à 60%
1% of Original amount = $250 ÷ 100 = $2.50
60% à 60 × $2.50 = $150 Ans: $150 left
Example4:
Ali bought a number of apples. He sold 70% of
the apples after which he had 120 apples left. How many apples did he buy?
Original number à 100%
Sold à 70%
Left à 30% (120)
1% of Original number =
120 ÷ 30 = 4
100% à 100 × 4 = 400
Ans: 400 apples
Per1:
Alan and Ben had 245 stamps altogether. Alan
had 25% fewer stamps than Ben. How many stamps did Ben have?
