SOLUTION: The average age of boys & girls in a class is 10.5 yrs. That of the boys is 10.6 & that of the girls is 10.1. If there are 60 boys in the class how many girls are there?

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Question 323609: The average age of boys & girls in a class is 10.5 yrs. That of the boys is 10.6 & that of the girls is 10.1. If there are 60 boys in the class how many girls are there?
Found 2 solutions by mananth, Fombitz:
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
let the number of girls be x
Number of boys = 60
Total students = x+60
Average age of class = 10.5
The total age of the class = 10.5(x+60)
..
Average age of girls = 10.1
total age of girls = 10.1x
..
Average age of boys = 10.6
Number of boys = 60
Total age of boys = 10.6*60= 636 years
..
Total age of girls + total age of boys = Total age of class
10.1x+636=10.5(x+60)
10.1x +636=10.5x + 630
10.5x-10.1x = 636-630
0.4x= 6
x= 6/0.4
Multiply by 10 and divide by 10
x=60/4
x=15 girls

Answer by Fombitz(32388) About Me  (Show Source):
You can put this solution on YOUR website!
Let B be the sum of ages of the boys, G sum of ages of the girls.
Let Nb be the number of boys, Ng be the number of girls.
1.B%2FNb=10.6
2.G%2FNg=10.1
3.%28B%2BG%29%2F%28Nb%2BNg%29=10.5
Nb=60
Then from eq. 1,
B=60%2810.6%29
B=636
From eq. 2,
G=10.1%2ANg
Substitute into eq. 3,
%28B%2BG%29%2F%28Nb%2BNg%29=10.5
B%2BG=10.5%2ANb%2B10.5%2ANg
B%2B10.1%2ANg=10.5%2ANb%2B10.5%2ANg
10.6%2ANb%2B10.1%2ANg=10.5%2ANb%2B10.5%2ANg
0.1%2ANb=0.4%2ANg
Ng=Nb%2F4
Ng=60%2F4
highlight%28Ng=15%29