Solution: (A + B + C)'s 1 day's work = (1/24 + 1/6 + 1/12) = 7/24

So, A, B and C together will complete the job in 24/7 = 3 3/7 days.

Workspace

16.

A man can do a job in 15 days. His father takes 20 days and his son finishes it in 25 days. How long will they take to complete the job if they all work together? [Hotel Management 2003]

The son alone can do the work in 15/2 = 7 1/2 days

Workspace

18.

A can lay railway tracks between two given stations in 16 days and B can do the same job in 12 days. With the help of C, they did the job in 4 days only. Then , C alone can do the job in: [S.S.C 2003]

A's 1 day's work = 1/16
B's 1 day's work = 1/12
C's 1 day's work = 1/4 - (1/16 + 1/12) = (1/4 - 7/48) = 5/48

So, C alone can do the work in 48/5 = 9 3/5 days

Workspace

19.

A takes twice as much time as B or thrice as much time to finish a piece of work. Working together, they can finish the work in 2 days. B can do the work alone in: [S.S.C. 2002]

Solution: Whole work will be done by X in (10 * 4) = 40 days
Whole work will be done by Y in [40 * (100/40)] = 100 days.
Whole work will be done by Z in (13 * 3) = 39 days

Z will complete the work first.

Workspace

21.

P, Q and R are three typists who working simultaneously can type 216 pages in 4 hours. In one hour, R can type as many pages more than Q as Q can type more than P. During a period of five hours, R can type as many pages as P can during seven hours. How many pages does each of them type per hour?