When 18 boys Joined a group of y students, the Ratio of boys to girls in the group became 4:5. Write an algebraic expression for the number of girls in terms of y.

Boys + Girls = y

(B + 18) : G = 4 : 5

5 (B + 18) = 4 g

5 B + 90 = 4 G

5 B = 4 G - 90 / : 5

B = 4/5 G - 18

Then:

4/5 G - 18 + G = y

9/5 G = y + 18 / * 5/9

G = 5 * (y + 18) / 9

Answer:

Number of girls in terms of y is:

G = 5/9 y + 10