There are 138 children in a school field.
38 of the boys and
47 of the girls wear watches, there are 78 children in the school field who do not wear watches. How many girls do not wear watches?
| |
Boys |
Girls |
Total |
| Do not wear watches |
5 u |
3 p |
78 |
| Wear watches |
3 u |
4 p |
60 |
| Total |
8 u |
7 p |
138 |
Number of children who wear watches
= 138 - 78
= 60
5 u + 3 p = 78 --- (1)
3 u + 4 p = 60 --- (2)
Make u the same.
(1)
x 3 15 u + 9 p = 234 --- (3)
(2)
x 5 15 u + 20 p = 300 --- (4)
(4) - (3)
(15 u + 20 p) - (15 u + 9 p) = 300 - 234
20 p - 9 p = 66
11 p = 66
1 p = 66 ÷ 11 = 6
Number of girls who do not wear watches
= 3 p
= 3 x 6
= 18
Answer(s): 18
