Question

In September, the total enrollment of a school was 1.200

students. Of these students, 20% of them were boys. In
October, some more boys enrolled in the school and the
percent of students that are boys changed to 25% How many
boys enrolled in the school in October?

Answer 1

80 boys

Explanation:

The number of boys that enrolled in September is 1200*20%. 20%=.2 so 1200*.2=240 boys enrolled. Then you can write an equation for the boys that enrolled in October.
`(240+x)/(1200+x)` = 25%. 25% is the same thing as 25/100 which simplifies down to 1/4. Once you cross multiply, you get 4*(240+x)=1200+x. Expanding the left side gives you 960+4x=1200+x. Subtracting 960 from both sides gives you 4x=240+x. Subtracting x from both sides gives you 3x=240. Dividing both sides by 3 gives you the answer x=80.