21.

A can do piece of work in 30 days while B alone can do it in 40 days. In how many days can A and B working together do it?

 A. 16 1 7 B. 17 1 7 C. 18 1 7 D. 19 1 7
Explanation: A can finish his work in 30 days B can finish his work in 40 days Therefore A’s one day’s work = 1 30 B’s one day’s work = 1 40 (A+B)’s one day’s work = 1 30 + 1 40 4+3 120 = 7 120 Number of days required for A and B to finish the work = 1 ( 7 120 ) = 120 7 =17 1 7 days

22.

To complete a piece of work A and B take 8 days, B and C 12 days. A, B and C take 6 days. A and C will take :

 A. 7 Days B. 7.5 Days C. 8 Days D. 8.5 Days
Explanation: Given (A+B)’s one day’s work = 1 8 (B+C)’s one day’s work = 1 12 (A+B+C) ‘s 1 day’s work = 1 6 Work done by A, alone= (A+B+C) ‘s 1 day’s work - (B+C)’s one day’s work = 1 6 – 1 12 = 2−1 12 = 1 12 Work done by C, alone = (A+B+C) ‘s 1 day’s work - (A+B)’s one day’s work = 1 6 – 1 8 = 4−3 24 = 1 24 ⇒ (A+C)’s one day’s work = 1 12 + 1 24 = 2+1 24 = 3 24 = 1 8 ⇒ (A+C) will take 8 days to complete the work together.

23.

Two pipes can fill the cistern in 10hr and 12 hr respectively, while the third empty it in 20hr. If all pipes are opened simultaneously, then the cistern will be filled in

 A. 7.5 hr B. 8 hr C. 8.5 hr D. 10 hr
Explanation: Work done by all the tanks working together in 1 hour. ⇒ 1 10 + 1 12 − 1 20 = 2 15 Hence, tank will be filled in 15 2 = 7.5 hour.

24.

Mr. Ram is on tour and he has Rs 360 for his expenses. If he exceeds his tour by 4 days he must cut down daily expenses by Rs 3. The number of days of Mr. Ram's tour programme is

 A. 28 Days B. 24 Days C. 22 Days D. 20 Days