66
Percent
Textbook: Part 2, lesson 66, pp. 121–125
GoalThe idea of percent; finding a percent of a number; finding a number from its percent; finding what percent one number is of another.
New words
percent (%) · foiz (%)one hundredth · yuzdan bir ulushprice reduction · arzonlashtirishprice increase · qimmatlashtirish
Explanation
One hundredth of a quantity is called one percent of it: 1% = 1/100 = 0.01, and the whole quantity is 100%. To find p percent of a number, divide it by 100 (this gives 1%) and multiply by p, that is, multiply the number by p/100. If p percent of a number is known, divide the known amount by p to get 1%, then multiply by 100 to find the whole. To find what percent one number is of another, divide one by the other and multiply the result by 100: 18 : 24 = 0.75 = 75%. If a price is reduced by 10%, the new price is the old price minus 10% of the old price.
Worked examples
20% of 350: 350 : 100 = 3.5 (1%); 3.5 · 20 = 70. Finding the whole: if 15% is 45, then 1% = 45 : 15 = 3 and 100% = 3 · 100 = 300.
What percent of 24 is 18: 18 : 24 = 0.75 = 75%. An item costing 80 000 so‘m is reduced by 10%: 80 000 : 100 · 10 = 8 000; new price 80 000 − 8 000 = 72 000 so‘m.
Class activity
“Discounts”: with an adult, find 3 prices and discount percentages in a shop or advert and calculate the new prices. Which discount saves the most money?
Practice
1
Find 40% of 250.
100
2
12% of a number is 60. Find the number.
500
3
What percent of 12 is 9? (write without the % sign)
75
4
Why is 50% equal to half of the whole?
50% = 50/100 = 1/2.