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07 Jan 2020, 07:14
Kudos
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
95%
(hard)
Question Stats:
27% (02:17) correct
73%
(01:39)
wrong
based on 172
sessions
History
Date
Time
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Not Attempted Yet
A can build an entire wall in 50 days whereas B, who is a demolition man, can break the entire wall in 60 days. If they work on alternate days with A starting, in how many days will the wall be built completely for the first time?
A. 299
B. 300
C. 589
D. 599
E. 600
A. 299
B. 300
C. 589
D. 599
E. 600
Updated on: 10 Jan 2020, 02:12
Originally posted by CareerGeek on 10 Jan 2020, 01:42.
Last edited by CareerGeek on 10 Jan 2020, 02:12, edited 1 time in total.
Last edited by CareerGeek on 10 Jan 2020, 02:12, edited 1 time in total.
Kudos
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Bunuel
Let the total number of bricks the wall has = LCM(50, 60) = 300
--> Rate of A (number of bricks built in a day), \(R_A\) = 300/50 = 6 bricks/day
--> Rate of B (number of bricks demolished in a day), \(R_B\) = 300/60 = 5 bricks/day
So, in 2 days, effective number of bricks built = 6 - 5 = 1
Number of bricks built in 588 days = 588/2 = 294
--> Number of bricks built the next day i.e. day 589 = 294 + 6 = 300
IMO Option C
10 Jan 2020, 02:08
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Just used smart numbers, no need to add the number of bricks IMHO you already have a rate with the days...
300 sounded like a bet good ol' fat rounded number.
in those 300 days A builds 6 walls, B destroys 5 walls. Sounds about right
If you pick other answers like 600 the rate of walls built will increase (in this case by one)
ANSWER B
300 sounded like a bet good ol' fat rounded number.
in those 300 days A builds 6 walls, B destroys 5 walls. Sounds about right
If you pick other answers like 600 the rate of walls built will increase (in this case by one)
ANSWER B
