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22 Aug 2019, 23:41
Kudos
Bookmarks
A can build a wall in 6 hours while B can demolish the same wall in 10 hours In how many hours would A be able to build the wall if they work on alternate hours?
My attempt:
After this how to proceed?
My attempt:
total work 30 units
A's efficiency = 5
B efficiency = - 3
--------------------------------------
Combining gives me: 2 hours = 2 Units.
A's efficiency = 5
B efficiency = - 3
--------------------------------------
Combining gives me: 2 hours = 2 Units.
After this how to proceed?
23 Aug 2019, 15:56
Kudos
Bookmarks
Hi kingston123,
Are you currently studying for the GMAT or is this question for some other Test or class? I ask because this question is not written in proper GMAT 'style' (and does not include the answer choices) and the logic behind it is not something that you will likely see on the GMAT.
That having been said, here's how you can solve it:
"A" can build 1/6 of the wall per hour.
"B" can destroy 1/10 of the wall per hour.
Thus, after A works for 1 hour and B works for 1 hour...
1/6 - 1/10 =
10/60 - 6/60 =
4/60 = 1/15 of the wall will be built.
After 14 hours for A and 14 hours for B, 14/15 of the wall will be complete. Since A completes 1/6 of the wall in 1 hour, and only 1/15 of the wall remains to be built, A would NOT have to work an additional hour. It would take:
(1/15)/(1/6) = (6/15)/(6/6) = .4/1 = .4 additional hours --> 24 additional minutes on top of the 14 prior hours.
GMAT assassins aren't born, they're made,
Rich
Are you currently studying for the GMAT or is this question for some other Test or class? I ask because this question is not written in proper GMAT 'style' (and does not include the answer choices) and the logic behind it is not something that you will likely see on the GMAT.
That having been said, here's how you can solve it:
"A" can build 1/6 of the wall per hour.
"B" can destroy 1/10 of the wall per hour.
Thus, after A works for 1 hour and B works for 1 hour...
1/6 - 1/10 =
10/60 - 6/60 =
4/60 = 1/15 of the wall will be built.
After 14 hours for A and 14 hours for B, 14/15 of the wall will be complete. Since A completes 1/6 of the wall in 1 hour, and only 1/15 of the wall remains to be built, A would NOT have to work an additional hour. It would take:
(1/15)/(1/6) = (6/15)/(6/6) = .4/1 = .4 additional hours --> 24 additional minutes on top of the 14 prior hours.
GMAT assassins aren't born, they're made,
Rich
23 Aug 2019, 19:26
Kudos
Bookmarks
EMPOWERgmatRichC
It would take: (1/15)/(1/6) = (6/15)/(6/6) = .4/1 = .4 additional hours --> 24 additional minutes on top of the 14 prior hours.
Answer is 26(4/5).
How to achieve it?
