algebra
posted by maxy .
there was a total of 840 guests at a wedding dinner. 60% of them were adults, and the rest were children. some boys left before the dessert was served. as a result, the percentage of adults increased to 70%. how many boys left before the dessert was served

original:
840 total
504 adults
336 children
final
840  b total
504 adults
336  b children
so
504 adults = .7(840 b)
all set? 
b=132

120 boys left before dessert was served

60% = 504
30% = 336
Solve by Proportion
504/336x = 7/3
2352  7x = 1512
7x = 840
x = 120