capacity of A doing work is double than B.if both together finish a work in 21 days,then A alone in how much days can finish the work? Choose the correct choice from the following
A) 16
B) 18
C) 15
D) 20
E) 21
let A alone can finish the work in x days.then B alone can finish the work in 2x days.   work of A in 1 days=1/x,and work of 18 in 1 days=1/2x   (A+18) work in 1 days=[1/x+1/2x]=3/2x   but,(A+18) work in 1 days=1/12   3/2x=1/12,2x=36,x=18   answer 18
<result>B</result>
capacity of A doing work is double than B.if both together finish a work in 21 days,then A alone in how much days can finish the work?