This is 22 points initially, $40\%$ of the students at the school dance are girls. then, $15$ more girls arrive, after which $52\%$ of the students at the dance are girls. how many students are now at the dance after the additional girls arrive?

Let the initial number of girls be x, this represents 40% of the dancers.
Total number of dancers will therefore be:
100/40*x=2.5x
When 15 more girls joined, the new number of girls was:
x+15 this represents the total percentage of 52%. The new number of dancers became:
2.5x+15:
therefore the new percentage of girls can be expressed as follows:
(new number of girls)/(new number of dancers)×100
(x+15)/(2.5x+15)×100=52
(x+15)/(2.5x+15)=0.52
x+15=0.52(2.5x+15)
x+15=1.3x+7.8
15-7.8=1.3x-x
7.2=0.3x
x=7.2/0.3=24
The number of students after additional number of girls will be:
2.5x+15
=2.5×24+15
=60+15
=75 students

25% increaseplus i think decrease i only know increase: ((