The average height of some boys is 139 cm. When 3 girls, with a total height of 354 cm, are included, the average height if the children becomes 130 cm. How many children are there altogether?
|
Boys |
Girls |
Total |
Number |
1 u |
3 |
1 u + 3 |
Value |
139 |
|
130 |
Total value |
139 u |
354 |
130 u + 390 |
Total height of the boys
= 1 u x 139
= 139 u
Total height of the children = 139 u + 354
139 u + 354 = 130 u + 390
139 u - 130 u = 390 - 354
9 u = 36
1 u = 36 ÷ 9 = 4
Total number of children
= 1 u + 3
= 4 + 3
= 7
Answer(s): 7