771. P takes twice as much time as Q or thrice as much time as R to finish a piece of work. They can finish the work in 2 days if work together. How much time will Q take to do the work alone?
A. 7
B. 8
C. 9
D. 6

Explanation
Let P takes x days to complete the work
Then Q takes x/2 days and R takes x/3 days to finish the work
Amount of work P does in 1 day = 1/x
Amount of work Q does in 1 day = 2/x
Amount of work R does in 1 day = 3/x
Amount of work P,Q and R do in 1 day = 1/x + 2/x + 3/x = 1/x (1 + 2 + 3) = 6/x
6/x = 2
=> x = 12
=> Q takes 12/2 days = 6 days to complete the work

772. 3 men and 7 women can complete a work in 10 days . But 4 men and 6 women need 8 days to complete the same work . In how many days will 10 women complete the same work?
A. 50
B. 30
C. 40
D. 13

Explanation
Work done by 4 men and 6 women in 1 day = 1/8
Work done by 3 men and 7 women in 1 day = 1/10
Let 1 man does m work in 1 day and 1 woman does w work in 1 day. The above equations can be written as
4m + 6w = 1/8 —(1)
3m + 7w = 1/10 —(2)
Solving equation (1) and (2) , we get m=11/400 and w=1/400
Amount of work 10 women can do in a day = 10 × (1/400) = 1/40
Ie, 10 women can complete the work in 40 days

773. P, Q and R can do a work in 20, 30 and 60 days respectively. How many days does it need to complete the work if P does the work and he is assisted by Q and R on every third day?
A. 10 days
B. 14 days
C. 15 days
D. 9 days

774. A tank can be filled by a pipe in 20 min. and by another pipe in 60 min. Both the pipes are kept open for 10 min. and then the first pipe is shut off. After this, the tank will be completely filled in__________?
A. 10 min
B. 20 min
C. 30 min
D. 40 min

775. A is thrice as good a work man as B and takes 10 days less to do a piece of work than B takes. B can do the work in:___________?
A. 15 days
B. 14 days
C. 16 days
D. 30 days

Explanation:
Ratio of times taken by A and B = 1 : 3
If the difference of time is 2 days, B takes 3 days. If the difference of time is 10 days.
B takes [3/2×10]=15 days

776. 8 children and 12 men complete a certain piece of work in 9 days. If each child takes twice the time taken by a man to finish the work, in how many days will 12 men finish the same work ?
A. 6 days
B. 8 days
C. 10 days
D. 12 days

Explanation:
2 children = 1 man
(8 children + 12 men ) = 16 men
Now, less men, more days
12 : 16 : 9 : x
x = 16×9/12=12 days

777. 15 men can build a 500m long wall in 30 days. In how many days can 30 men build a 1.2 km long wall?
A. 48 days
B. 24 days
C. 40 days
D. 36 days

Explanation:
No. of days is
directly proportional to the length of the wall and
inversely proportional to the number of men No. of days = (1200/500)*(15/30)*30 = 36 days

778. If 28 men can finish a work in 15 days, 21 men can finish the same work in___________?
A. 24 days
B. 14 days
C. 15 days
D. 20 days

Explanation:
Time and Men are inversely proportional. Time taken by 28 men to finish the work = 15 days Time taken by a man to finish the work
= 15*28 days Time taken by 21 men = (15*28)/21 = 20 days

779. C takes 6 days to complete half of a work and D takes 5 days to complete 1/3rd of the same work. They take turns to complete the task. If C works for the first 4 days, in how many days will D complete the rest of the work without the help of C?
A. 10 days
B. 12 days
C. 8 days
D. 9 days

Explanation:
Part of work completed by C in 1 day = 1/12 Part of work completed by D in 1 day = 1/15 Part of work completed by C in 4 days
= 1/3 Work remaining = 2/3 Time taken by D to complete the work
= (2/3)÷(1/15) = 10 days

780. P,Q and R together earn Rs.1620 in 9 days. P and R can earn Rs.600 in 5 days. Q and R in 7 days can earn Rs.910. How much amount does R can earn per day?
A. Rs.40
B. Rs.70
C. Rs.90
D. Rs.100

Explanation:
Amount Earned by P,Q and R in 1 day = 1620/9 = 180 —(1)
Amount Earned by P and R in 1 day = 600/5 = 120 —(2)
Amount Earned by Q and R in 1 day = 910/7 = 130 —(3)
(2)+(3)-(1) => Amount Earned by P , Q and 2R in 1 day
– Amount Earned by P,Q and R in 1 day = 120+130-180 = 70
=>Amount Earned by R in 1 day = 70

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