47. A and B can complete a work in 15 days and 10 days respectively. They started doing the work together but after 2 days B had to leave and A alone completed the remaining work. the whole work was completed in?

A. 8 days B. 10 days C. 10 1/2 days D. 12

Answer Answer: Option D Explanation: (A+B)'s 1 day's work = (1/15+ 1/10) = 1/6.
work done by A and B in 2 days = (1/6*2) = 1/3. Remaining work = ( 1- 1/3) = 2/3.
Now, 1/15 work is done by A in 1 day.
therefore 2/3 work will be done by A in (15*2/3) = 10 days.
hence, total time taken = (10+2) = 12 days.

48. A & B together can complete a piece of work in 4 days. If A alone can complete the same work in 12 days in how many days can B alone complete that work?

A. 7 days B. 5 days C. 6 days D. 9 days

Answer Answer: Option C Explanation: (A + B)'s 1 day's work = 1/4; A's 1 day's work = 1/12;
B's 1 day's work = (1/4 - 1/12) = 1/6
Hence B alone can complete the work in 6 days.

49. 45 men can complete a work in 16 days. Six days after they started working 30 more men joined them.How many days will they now take to complete the remaining work?

A. 5 days B. 7 days C. 8 days D. 6 days

Answer Answer: Option D Explanation: (45*16) men can complete a work in 1 day
1 man's 1 day's work = 1/720
45 men's 6 day's work =(1/16*6) = 3/8, Remaining work = ( 1- 3/8) = 5/8
75 men's 1 day's work = 75/720 = 5/48
Now 5/48 work is done by them in 1 day
5/8 work is done by them in(48/5*5/8) = 6 days

50. 2 men and 3 boys can do a piece of work in 10 days while 3 men and 2 boys can do the same work in 8 days.In how many days can 2 men and 1 boy do the work?

A. 13 1/2 days B. 13 days C. 12 1/2 days D. 10 days

Answer Answer: Option C Explanation: Let 1 man's 1 day's work = x and 1 boy's 1 day's work = y then,
2x+3y = 1/10 and 3x+2y = 1/8
solving we get : x= 7/200 and y = 1/100
(2 men + 1 boy)'s 1 day work = (2*7/200+ 1*1/100) = 16/200 = 2/25
so 2 men and 1 boy together can finish the work in 25/2 = 12 1/2 days.