Question 900941
rate for A alone 4
rate for A & B together 2.5
1/a+1/b=1/x
1/4+1/b=1/2.5
1/b=1/2.5-1/4
1/b=4/10.0-2.5/10.0
1/b=1.5/10.0
1/b=1/6.66666667
b=6.66666667
rate for B alone 6.66666667