Let the men do the work in a days and the boys in b days.
∴ (3/a) + (4/b) = 1/8 ..... (i)
Now, 6/a + 8/b = 2[(3/a) + (4/b)] = 2 x 1/8 = 1/4

Correct Option: B

Let the men do the work in a days and the boys in b days.
∴ (3/a) + (4/b) = 1/8 ..... (i)
Now, 6/a + 8/b = 2[(3/a) + (4/b)] = 2 x 1/8 = 1/4
So, 6 men and 8 boys can do the same work in 4 days.

A's 1 day's work = 1/6
B's 1 day's work = 1/12
(A + B)'s 1 day's work = 1/6 + 1/12 days

Correct Option: D

A's 1 day's work = 1/6
B's 1 day's work = 1/12
(A + B)'s 1 day's work = 1/6 + 1/12
= (2 + 1)/12 = 3/12 = 1/4
Hence, both will complete the work in 4 days.

We have the important relation, More work, More time (days)
∵ A piece of work can be done in 6 days.
∴ Three times of work of same type can be done in 6 x 3

Correct Option: A

We have the important relation, More work, More time (days)
∵ A piece of work can be done in 6 days.
∴ Three times of work of same type can be done in 6 x 3
= 18 days

(A + B)'s 1 days work = 1/12
B's 1 days work = 1/30
∴ A's 1 days work = 1/12 - 1/30 = (5 - 2)/60 = 1/20

Correct Option: C

(A + B)'s 1 days work = 1/12
B's 1 days work = 1/30
∴ A's 1 days work = 1/12 - 1/30 = (5 - 2)/60 = 1/20
∴ A alone can finish the work in 20 days.

A's 1 day's work = 1/18
B's 1 day's work = 1/9

Correct Option: A

A's 1 day's work = 1/18
B's 1 day's work = 1/9
(A + B)'s 1 day's work = 1/9 + 1/18 = 3/18 = 1/6