There are 4 more girls in Mrs. Chang's class than Mr. Blackwell's class. Five girls moves from Mr. Chang's class to Mr. Blackwell's class. Now there are twice as many girls in Mr. Blackwell's class as there are in Mrs. Chang's. How many girls were in Mr. Blackwell's class to begin with?

Answer 1

Mr. B. Class: X $Girls.
Mr. C. Class:: (x+4) Girls.

Mr. B. Class: (x+5).
Mr. C. Class: (x+4) - 5 = (x-1).

(x+5) = 2(x-1)
x+5 = 2x - 2
x-2x = -2 -5 = -7
-x = -7
X = 7 Girls to begin with.