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Probability & Work question

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Senior | Next Rank: 100 Posts
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by ramyaravindran » Sat Jan 16, 2010 3:30 pm
Can you please help with these questions below? Thanks.

1. There are 6 seats in a row and 3 married couples need to be seated in such a way that the couples always sits together. In how many ways can this be done?

2. A can complete a certain task in 4 hours. B can complete the same task in 6 hours and C can complete the same task in 8 hours. If A,B and C work together to complete the task then what percentage of work was done by A?
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by ace_gre » Sat Jan 16, 2010 6:14 pm
Hi, Here is my approach..

1. Let the seats be numbered 1 to 6 and the three couples be represented as ABC.

Consider the available seats for the couples as 1,3 and 5. No. of ways the couples can be seated is 3!. Also each couple can be seated in 2!. So total number of seating arrangements = 3! *2!*2!*2! = 48.

IMO 48

2. A can complete 1 job in 4 hrs
A can complete 1/4 job in 1 hr --------(1)
B can complete 1/6 job in 1hr
C can complete 1/8 job in 1 hr.

Total work done by A,B and C in 1 hr = 1/4 +1/6 + 1/8 = 13/24-----(2)

% of work done by A = (1/4) / (13/24) ~ 46%

IMO 46%

Please post OA. Thanks!
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by ramyaravindran » Sun Jan 17, 2010 12:07 pm
Thanks ace_gre. You have the right answer for both the questions.
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