Answer: Option C

Explanation:
work done by 1 hour by filling pipe = 1/8
work done by 1 hour by the leak and the filling pipe =1/12
work done by 1 hour by the leak = 1/8 – 1/12 =1/24
Hence the leak can empty it in 24 hours. 

Answer: Option B

Explanation:
A and B 2 hours work = 1/12 + 1/18 = 5/36
work done by A and B during 6 pairs
i.e 12 hours = 6  * 5/36 = 5/6
Remaining work = 1 – 5/6 = 1/6
1/6 of work and this work done by B only = 18* 1/6 = 3 hours
Hence the total time take is  15 hours

Answer: Option C

Explanation:
(A+B) 1 day work = 1/48
(B+C) 1 day work = 1/72
(A+C) 1 day work = 1/60
By adding 2(A+B+C) = 1/48 +1/72+1/60 = 37/720
(A+B+C) 1 day work = 37/1440
A 1 day work = 37/1440 – 1/72 = 17/1440 = 85 days (approximately)    

Answer: Option

Explanation:
1 boy 1 day work = 14 × 8, 
14 boys complete the work in 14 × 8/14= 8 days   

Answer: Option C

Explanation:
16 boys =24 girls, 1 boy =  24/16 girls
                           1 boy = 6/4 girls
8 boys + 12 girls = 8 × 6/4 + 12 = 12 + 12 = 24 girls
6 days to complete the work

Answer: Option C

Explanation:
(6dogs+8cats) 1 day work = 1/12
(5dogs+8cats) 1 day work = 1/16
substract 1 and 2
i.e 1/12 – 1/16= 1/48
i.e 1 dog 1 day work is 1/48
4dogs + 8cats  1day work is 1/16 – 1/48 = 1/24
thus 4 dogs and 8 cats will finish it in 24 days

Answer: Option A

Explanation:
Let ‘x’ be the number of days taken by B alone to finish the whole work 
Then, A alone will finish the whole work in 3x/4 × 2 days = 3x/2 days. 
Then, working together, 
               3x/2 × x/3x/2 + x = 18 days 
               3x × x/5x = 18 
               3x/5 = 18 
             Therefore, the number of days taken by B = x = 18 × 5/3 = 30 days.

Answer: Option A

Explanation:
Both of them together can finish the work (daily working) in 12 × 18/30 days = 36/5 
                                                                                                              = 7 1/5 days. 
By working in alternate days, their 2 day’s work = 5/36 
Their, 14 day’s work (because they take more than double of 7 days) = 5/36 × 7 
                                                                                           = 35/36 
Remaining work = 1 – 35/36 = 1/36 
Because A started the work, the remaining work is finished by A 
A’s 1 day’s work = 1/12 
Therefore, the No. of days taken by A to finish 1/36 work = 1/36/1/12 = 1/3 days. 
Therefore, the total work is completed in 14 + 1/3 = 14 1/3 days.

Answer: Option C

Explanation:
B’s 1 day’s work = 1/21
B’s 3 day’s work = 1/21 ×3 = 1/7 
The remaining work finished by both of them = 1 – 1/7 = 6/7 
Both together can finish it in 14 × 21/35 days = 42/5 days 
Their, 1 day’s work = 5/42 
Therefore, the No. of days taken by them together to finish 6/7 work 
                                                  = 6/7/5/42 = 6/7 × 42/5 =  36/5 = 7 1/5 days 
Therefore, the total No. of days for the work to be completed = 3 + 7 1/5 = 10 1/5 days.

Answer: Option D

Explanation:
(A + B)’s 1 day’s work = 1/30 
Their 20day’s work = 1/30 × 20 = 2/3 
Remaining 1/3 work is done by A in 20 days 
Therefore, A alone can finish the work in 3 × 20 = 60 days.