<PRE><B>Question 970249</B>
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,
{{{35/100 = (G/(all pupils))}}}
{{{35/100 = (G/(B+G))}}}
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
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