16
Finding a part of a number
Textbook, pp. 65–67
GoalFind a part of a number: calculate the value given by a fraction.
New words
part of a number · sonning qismishare / fraction part · ulushpercent · foizwhole · butun
Explanation
To find a part of a number, multiply the number by the fraction. For example, 3/5 of 40 is 40 · 3/5 = 24. It is convenient to do this in two steps: first divide 40 by 5 (this is 1/5), then multiply by 3. A percentage is also a fraction: 25% = 1/4 and 50% = 1/2. So a percentage of a number is found in the same way. The word “of” often means multiplication.
Worked examples
3/4 of 120 books: 120 : 4 = 30, and 30 · 3 = 90 books.
25% of 80: 25% = 1/4, and 80 : 4 = 20.
Class activity
“Find the part”: pupils work in teams. The teacher says “2/3 of 36 apples!”; teams split counters or cards into equal groups and show the answer.
Practice
1
Find 3/4 of 120.
90
2
Find 2/5 of 35.
14
3
A class has 32 pupils and 3/8 of them are boys. How many boys are there?
12
4
Is 3/4 of a number bigger or smaller than the number? Why?
Smaller, because 3/4 < 1: we take only a part of the number.