46
Review problems
Textbook: Part 2, lesson 46, pp. 38–39
GoalReview the chapter so far: circle and disc, fractions, comparing, adding and subtracting.
New words
radius and diameter · radius va diametrfraction · kasrcomparing fractions · kasrni taqqoslashunit segment · birlik kesma
Explanation
All points of a circle are the same distance from its centre; the diameter is 2 times the radius. A fraction shows into how many equal shares the whole was divided (denominator) and how many were taken (numerator). Of fractions with the same denominator, the one with the larger numerator is larger; a proper fraction is less than 1, an improper one is at least 1. To find a part of a number, divide it by the denominator and multiply by the numerator. The fraction line means division; when fractions with the same denominator are added or subtracted, the denominator stays the same.
Worked examples
A circle of radius 7 cm has diameter 7 · 2 = 14 cm. Adding 2/5 and 4/5 gives 6/5, an improper fraction (greater than 1).
If 3/4 of a number is 15: 15 : 3 = 5, 5 · 4 = 20. The number itself is 20.
Class activity
“Fraction game”: write 1/6, 5/6, 6/6, 7/6, 3/6 on cards. Arrange them in increasing order and say which are proper and which improper.
Practice
1
What is the radius (cm) of a disc with diameter 18 cm?
9
2
Find 3/8 of 64.
24
3
Calculate 11/14 − 4/14 + 2/14.
9/14
4
Why is the sum 5/8 + 4/8 an improper fraction?
5/8 + 4/8 = 9/8: its numerator (9) is larger than its denominator (8), so the sum is greater than 1.