Solution
30% of 30 is written as
30% × 30 = (30 / 100) × 30 = 900 / 100 = 9
150% of 60 =
Solution
150% of 60 is written as
150% × 60 = (150 / 100) × 60 = (150 × 60) / 100 = 90
1/4 =
4%
1%
0.25%
25%
Solution
We need to change the fraction 1 / 4 into a fraction with denominator 100 which is a percent
1 / 4 = (1 × 25) / (4 × 25) = 25 / 100 = 25%
0.05 =
50%
500%
5%
0.5%
Solution
We need to change the decimal number 0.05 into a fraction with denominator 100 which is a percent
0.05 = 0.05 / 1 = (0.05 × 100) / (1 × 100) = 5 / 100 = 5%
If 100% of a number is 15, what is 50% of the number?
Solution
Let n be the number
100% of a number is 15 is written as: 100% × n = 15
100% = 100 / 100 = 1
Hence
100% × n = n = 15
We now need to find 50% of the number
50% of 15 = (50 / 100) × 15 = 750 / 100 = 7.5
NOTE that the above problem could be solved by noting that 50% of something is half of 100% of the same thing. Hence if 100% of something is 15 then 50% of the same thing is haflf of 15 / 2 = 7.5
If 10% of a number is 7, what is 80% of the number?
Solution
Note that 80% of something is 8 times 10% of the same thing. Hence if 10% of a number is 7 then 80% of the same number is given by
8 × 7 = 56
Which is the greatest?
90% of 10
6% of 1000
5% of 1400
3% of 2500
Solution
Express as fractions with same denominator 100 and then compare
90% of 10 = (90 / 100) × 10 = 900 / 100
6% of 1000 = (6 / 100) × 1000 = 6000 / 100
5% of 1400 = (5 /100) × 1400 = 7000 / 100
3% of 2500 = (3 / 100) × 2500 = 7500 / 100
The largest fraction is 7500 / 100 which correspond to 3% of 2500. Hence 3% of 2500 is the largest.
The original price of a toy was $15. If the price is reduced by 20%, what is the new price of the toy?
Solution
20% of price is
20% × 15 = $3
The original price was $15 and was reduced by 20% or $3. Hence the new price after reduction is
15 - 3 = $12
George bought a car at $5000 and sold it at $5500. What benefit, in percent, did he make?
Solution
The benefit in dollars is
$5500 - $5000 = $500
Express $500 as a percent of $5000 as follows
500 / 5000 = 5 / 50 = 10 / 100 = 10%
If 20% of n is equal to 40, what is n?
Solution
"20% of n is equal to 40" is written as
20% × n = 40
(20 / 100) × n = 40
Rewrite the above with fraction on the right side with denominator equal to 100
20 n / 100 = 40 / 1 = 4000 / 100
Since the two fractions have same denominator and are equal, their numerator must be equal. Hence
20 n = 4000 which means that n = 200.
200
2000
800
80
The price of a T-shirt was $20. It was first increased by 20%. They did not sell well the shop owner decreased the price by 20%. What is the new price of the T-shirt?