If A is thrice as fast as B and together can do a work in 21 days. In how many days A alone can do the work?
36 days
42 days
28 days
54 days
Explanation:
let 'x' be the number of days worked by 'A'
A = 3x
B = x
=>1/3x + 1/x = 1/21
=>4/3x = 1/21
=>3x = 21*4
=>x = (21*4)/3
=>x = 7*4
=>x = 28
Hence, 'A' can do the same work alone in 28 days.
let 'x' be the number of days worked by 'A'
A = 3x
B = x
=>1/3x + 1/x = 1/21
=>4/3x = 1/21
=>3x = 21*4
=>x = (21*4)/3
=>x = 7*4
=>x = 28
Hence, 'A' can do the same work alone in 28 days.