Time and Work
 A can finish a work in 7 days. B can finish the same work in 9 days. The number days required to finish the same work by both of them together is

View Hint View Answer Discuss in Forum
A’s 1 day’s work = 1 7 B’s 1 day’s work = 1 9
∴ (A + B)’s 1 day’s work= 1 + 1 7 9 = 1440 = 40 = 3 1 days 468 13 13 ∴ Required time = 63 days 16 = 3 15 days 16 Correct Option: C
A’s 1 day’s work = 1 7 B’s 1 day’s work = 1 9
∴ (A + B)’s 1 day’s work= 1 + 1 7 9 = 1440 = 40 = 3 1 days 468 13 13 ∴ Required time = 63 days 16 = 3 15 days 16
 A, B and C working separately can do a piece of work in 11 days, 20 days and 55 days respectively. In how many days, the work will be completed if A is assisted by B and C on alternate days ?

View Hint View Answer Discuss in Forum
(A + B)’s 1 day’s work
= 1 + 1 11 20 = 20 + 11 = 31 220 220
(A + C)’s 1 day’s work= 1 + 1 11 55 = 5 + 1 = 6 55 55
Work done in first two days= 31 + 6 220 55 = 31 + 24 = 55 = 1 220 220 4
∴ Required time = 2 × 4 = 8 daysCorrect Option: D
(A + B)’s 1 day’s work
= 1 + 1 11 20 = 20 + 11 = 31 220 220
(A + C)’s 1 day’s work= 1 + 1 11 55 = 5 + 1 = 6 55 55
Work done in first two days= 31 + 6 220 55 = 31 + 24 = 55 = 1 220 220 4
∴ Required time = 2 × 4 = 8 days
 A can do a piece of work in 12 days and B in 24 days. If they work together, in how many days will they finish the work?

View Hint View Answer Discuss in Forum
(A + B)’s 1 day’s work
= 1 + 1 12 24 = 2 + 1 = 3 = 1 24 24 8
∴ Required time = 8 daysCorrect Option: D
(A + B)’s 1 day’s work
= 1 + 1 12 24 = 2 + 1 = 3 = 1 24 24 8
∴ Required time = 8 days
 A and B together can finish a job in 24 days, while A, B and C together can finish the same job in 8 days. C alone will finish the job in

View Hint View Answer Discuss in Forum
(A + B)’s 1 day’s work = 1 24 (A + B + C)’s 1 day’s work = 1 6 ∴ C’s 1 day’s work = 1  1 8 24 = 3  1 = 2 = 1 24 24 12
∴ Required time = 12 daysCorrect Option: A
(A + B)’s 1 day’s work = 1 24 (A + B + C)’s 1 day’s work = 1 6 ∴ C’s 1 day’s work = 1  1 8 24 = 3  1 = 2 = 1 24 24 12
∴ Required time = 12 days
 A and B together can do a piece of work in 6 days and A alone can do it in 9 days. The number of days B will take to do it alone is

View Hint View Answer Discuss in Forum
(A + B)’s 1 day’s work = 1 6 A’s 1 day’s work = 1 9 ∴ B’s 1 day’s work = 1  1 6 9 = 3  2 = 1 18 18
∴ Required time = 18 daysCorrect Option: A
(A + B)’s 1 day’s work = 1 6 A’s 1 day’s work = 1 9 ∴ B’s 1 day’s work = 1  1 6 9 = 3  2 = 1 18 18
∴ Required time = 18 days