27-8= 19
Professor X has two graduate students and Professor Y has three graduate students.
2x+3y= 19
x+y=8
2x+2y= 16
y=3
x=5
2. Solution: Suppose all X water pipes are open.
10 = x * 1/3+2x *( 1- 1/3)
10=x/3+4x/3
10=5x/3
30 = 5 times
x=6