7th grade math
posted by Mercedez .
There are 48 students in a school play. The ratio of boys to girls is 5:7. How many boys are in the school play? Explain how you found your answer.

I'd set up a proportion (ratio).
5/12 = b/48
12b = 240
b = 20 
Where did you get the 5/12 from when it's 5/7?

You're comparing the number of boys with the total.
5 + 7 = 12 
A school has 1800 students on its roll 40% of whom are girls how many boys are there in the school

on the question above the one with no answer i got that answer but my teacher says it is wrong who is right and how did you get this answer?