SOLUTION: 0.35 of the pupils in a class are girls.If they are 18 more boys than girls,how many boys are in the class?

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Question 970249: 0.35 of the pupils in a class are girls.If they are 18 more boys than girls,how many boys are in the class?
Found 2 solutions by Boreal, LinnW:
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
X=girls
X+18=boys
Total=2X+18
.35 =X/(2X18); the proportion of girls-number/total
35% are girls
Multiply both sides by 2X+18; 0.35*2x=.0.70x; 0.35*18=6.3
.70x + 6.30=x
Subtract. 0.70x from both sides
.3x=6.30
Divide by .3 both sides
X=21
X+18=39
Total is 60; 21 girls
(21/60)=0.35

Answer by LinnW(1048) About Me  (Show Source):
You can put this solution on YOUR website!
Let B be the number of boys, and G be the number of girls.
Since there are 18 more boys than girls,
B = G + 18
Since 0.35 are girls,
35%2F100+=+%28G%2F%28all+pupils%29%29
35%2F100+=+%28G%2F%28B%2BG%29%29
do cross products
100G = 35(B+G)
Now substitute ( G + 18 ) for B
100G = 35(G+18) + 35G
100G = 35G + 630 + 35G
100G = 70G + 630
add -70G to each side
30G = 630
Divide each side by 30
G = 21
Since B = G + 18
B = 21 + 18 = 39