Answer:
So the way to approach these is to look at the 2:5 as "parts". In total there are 7 parts (2+5). Because there are 7 parts and 140 students, you can divide 140 by 7, which means for each "part" there are 20 students. So then you can multiply, 2 parts male (40), 5 parts female (100). So there are 40 boys in that class.
