191 children are in a school.
15 of the girls and
17 of the boys wear glasses.
33 children wear glasses.
- How many girls are there?
- How many boys are there?
- How many children do not wear glasses?
|
Number |
Girls |
Boys |
Total |
191 |
5 u |
7 p |
Wear glasses |
33 |
1 u |
1 p |
No glasses |
|
4 u |
6 p |
(a)
Number of girls = 5 u
Number of boys = 7 p
5 u + 7 p = 191 --- (1)
1 u + 1 p = 33 --- (2)
(2)
x 5 5 u + 5 p = 165 --- (3)
(1) - (3)
(5 u + 7 p) - (5 u + 5 p) = 191 - 165
5 u + 7 p - 5 u - 5 p = 26
2 p = 26
1 p = 26 ÷ 2 = 13
Substitute 1 p = 13 into (2).
1 u + 1 p = 33
1 u + 13 = 33
1 u = 33 - 13 = 20
Number of girls
= 5 u
= 5 x 20
= 100
(b)
Number of boys
= 7 p
= 7 x 13
= 91
(c)
Number of girls who do not wear glasses
= 5 u - 1 u
= 4 u
Number of boys who do not wear glasses
= 7 p - 1 p
= 6 p
Number of children who do not wear glasses
= 191 - 33
= 158
Answer(s): (a) 100; (b) 91; (c) 158