To figure out how many kids are in the school, you must set up an
equation with x representing the number of students. 30% of the students
are in the play, so that would be represented by 0.3x. We also know
that 140 students are not in the play, that could be represented by
x-140. These two equations will equal each other since they both
represent the same information, which is the number of children in the
play. You set those two equations equal to one another (0.3x = x-140).
You then can add 140 to the left side of the equation and subtract 0.3x
from the right side. We do this in order to get both values of x on the
same side of the equation. We then can simplify the right side of the
equation by subtracting 0.3x from 1x. We get 0.7x. Our equation now
looks like 140 = 0.7x. We must now divide each side of the equation by
0.7 in order to get the x all by itself and find its value. 140 divided
by 0.7 is 200. The number of students in the school is 200.
