Three classes in kindergarten have equal numbers, and the number of boys in class one is equal.

Let the number of students in each class be "1".

Because the number of boys in Class 1 and Class 2 is equal, the sum of boys in Class 1 and Class 2 and the sum of girls in Class 1 and Class 2 is equal to "1".

Let the number of boys in three classes be x, then x:(x+ 1)=2:5, and the solution is x=2/3.

So the number of girls in Class Three is 1-2/3= 1/3.

So the number of girls in Class Three is1/3/(1+1/3) =1/4.

That's a quarter.

References:

Liang's Olympic Mathematics Textbook