Question 903325
rate for A alone 11
rate for A & B together 10
1/a+1/b=1/x
1/11+1/b=1/10
1/b=1/10-1/11
1/b=11/110-10/110
1/b=1/110
1/b=1/110
b=110
rate for B alone 110
check
1/11+1/110=1/10
110/1210+11/1210=1/10
121/1210=1/10
ok