In a maths class of 26 students, each girl drew a triangle and each boy drew a rectangle. if there were 92 sides drawn by the students, how many girls were in the class?

Let there be x girls,   and y boys.

Since a triangle is 3 sides, the girls would draw 3x sides.

Since a rectangle is 4 sides, the boys would draw 4y sides.

Recall a total of 92 sides were drawn.

x + y = 26(a)

3x + 4y = 92(b)

From (a) y = 26 - x, substituting this into (b)

3x + 4*(26 - x) = 92

3x + 104 - 4x = 92

3x - 4x = 92 - 104

-x = -12

x = -12/-1 = 12.

Since x is the number of girls, so there are 12 girls