Difficult Math Problem #101

Expert replies

f2001290: Master | Next Rank: 500 Posts; Posts: 400; Joined: Sat Mar 10, 2007 4:04 amFollowed by: 1 member; Thanked: 1 times

by f2001290 » Sun May 27, 2007 7:31 am

John can complete a given task in 20 days. Jane will take only 12 days to complete the same task. John and Jane set out to complete the task by beginning to work together. However, Jane was indisposed 4 days before the work got over. In how many days did the work get over from the time John and Jane started to work on it together?

Soln:

Let x be the no. of days during which the work got over.
then

x(1/20) + (x-4)(1/12) = 1

Solving for x, we get x = 10
But OA is 6. Anything wrong with my solution?

Source: Beat The GMAT — Problem Solving | Sun May 27, 2007 7:31 am

jayhawk2001: Community Manager; Posts: 789; Joined: Sun Jan 28, 2007 3:51 pmFollowed by: 1 member; Location: Silicon valley, California; Thanked: 30 times

Re: Difficult Math Problem #101

by jayhawk2001 » Sun May 27, 2007 8:25 am

f2001290 wrote:John can complete a given task in 20 days. Jane will take only 12 days to complete the same task. John and Jane set out to complete the task by beginning to work together. However, Jane was indisposed 4 days before the work got over. In how many days did the work get over from the time John and Jane started to work on it together?

Soln:

Let x be the no. of days during which the work got over.
then

x(1/20) + (x-4)(1/12) = 1

Solving for x, we get x = 10
But OA is 6. Anything wrong with my solution?

I don't see anything wrong with your approach. 10 is indeed correct.

Please check https://www.beatthegmat.com/viewtopic.php?t=1585

f2001290: Master | Next Rank: 500 Posts; Posts: 400; Joined: Sat Mar 10, 2007 4:04 amFollowed by: 1 member; Thanked: 1 times

by f2001290 » Sun May 27, 2007 10:47 am

Thanks Jay

I was looking at cybermusing's solution. So, I was confused.

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