There were 60 children at the birthday party. 60% of the children were boys. When more boys arrived later, the percentage of girls decreased to 5%. How many boys arrived later?
Before the arrival
boys ---- 60% of 60 = 36
girls = 40% of 60 or 60-36 = 24
number of new boys = x
then 24/(x+60) = 5/100 = 1/20
x+60 = 480
x = 420
That's some birthday party!
check: after 420 boys arrive there are 480 children at the party, 24 of them girls
24/480 =.05 or 5%