Question 1172554

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b = number of boys
g = number of girls

b-8 = (2/3)g   (1)
2(g-8) = b     (2)

Substitute LHS of (2) for 'b' in (1):
2(g-8)-8 = (2/3)g
2g-24 = (2/3)g
6g-72 = 2g
   4g = 72  
    g = 18  -->(using (1) or (2))-->  b = 20

There are 20 boys and 18 girls in the class

Check:  
20 - 8 = 12 and 12 = (2/3)18   ((1) checks out)
2(18-8) = 2(10) = 20 = b       ((2) checks out)