In a class of 42 students, the number of boys is 2/5 of the girls. How do you find the number boys and girls in the class?

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Answer 1 · 2016-12-27T00:36:48

We turn that into equations:

(1) #B+G=42#

(2) #B=2/5xxG#

Replacing #B# by (2) we get:

#2/5xxG+G=1 2/5xxG=42#

Turning #1 2/5# into a non-mixed fraction:

#7/5xxG=42-># multiply by 5, divide by 7:

#G=42xx5/7=(6xxcancel7xx5)/cancel7=30#

#B=2/5xx30=2/cancel5xxcancel5xx6=12#

And these add up to 42.