21.  A can do a work in 7 days of 9 hours each and B can do it in 6 days of 7 hours each. How long will they take to do it working together 8 2/5 hours a day?


3 days
4 days
6 days
2 days


Answer

 Option

A can complete the work in = ( 7*9) = 63 hours B can complete the work in = ( 6*7) = 42 hours A's 1 hour's work = 1/63 and B's 1 hour's work = 1/42 (A + B)'s 1 hour's work = (1/63 + 1/42) = 5/126 = Number of days of 8 2/5 hours each = (126/5 * 5/42) = 3 days

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22.  A does half as much work as B in three-fourth of the time. If together they take 18 days to complete the work, how much time shall B take to do it?


30 days
35 days
40 days
none of these


Answer

 Option

Suppose B takes x days to do the work. therefore A takes (2*3/4 x) = 3x/2 days to do it. (A+B)'s 1 day's work = 1/18. therefore 1/x + 2/3x = 1/18 or x = 30.

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23.  Worker A takes 8 Hours to do a job. Worker B Takes 10 Hours to do the same job. How long should it take both A & B working together but independently to do the Same Job?


32/9
40/9
35/8
30/5


Answer

 Option

A's 1 Hour work=1/8, B's 1hour work =1/10 (A+B)'s 1 hour work =(1/8+1/10)=9/40. Both A & B Complete the work in 40/9 days

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24.  A takes twice as much time as B or thrice as much time to finish a piece of work. Working together, they can finish the work in 2 days. B can do the work alone in


4 days
6 days
8 days
12 days


Answer

 Option

Suppose A,B and C take x, x/2 and x/3 hours respectively to finish the work. Then, (1/x+ 2/x+3/x) = 1/2 = x = 12. so, B takes 6 hours to finish the work.

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25.  A and B can together finish a work in 30 days. They worked together for 20 days and then B left. After another 20 days, A finished the remaining work. In how many days A alone can finish the job?


40
50
54
60


Answer

 Option

(A+B)'s 20 days work = (1/30*20) = 2/3. Remaining work = (1- 2/3) = 1/3. Now, 1/3 work is done by A in 20 days. Whole work will be done by A in (20*3) = 60 days.

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