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If John can paint a room in 30 minutes and Tom can paint it
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03 Apr 2020, 08:24
03 Apr 2020, 08:24
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Question Stats:
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If John can paint a room in 30 minutes and Tom can paint it in 1 hour, how many minutes will it take them to paint the room working together?
A. 10
B. 15
C. 18
D. 20
E. 24
Kudos for the right answer and explanation
A. 10
B. 15
C. 18
D. 20
E. 24
Kudos for the right answer and explanation
Retired Moderator
Joined: 10 Apr 2015
Posts: 6218
Given Kudos: 136
Re: If John can paint a room in 30 minutes and Tom can paint it
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03 Apr 2020, 08:34
03 Apr 2020, 08:34
1
Carcass wrote:
If John can paint a room in 30 minutes and Tom can paint it in 1 hour, how many minutes will it take them to paint the room working together?
A. 10
B. 15
C. 18
D. 20
E. 24
Kudos for the right answer and explanation
A. 10
B. 15
C. 18
D. 20
E. 24
Kudos for the right answer and explanation
GIVEN:
John can paint a room in 30 minutes
Tom can paint a room in 60 minutes
A useful approach is to assign a "nice" value to the job.
We want a value that works well with the given information (30 minutes and 60 minutes).
So, let's say the entire job requires 60 brushstrokes
This means John can complete 60 brushstrokes in 30 minutes. So, John's RATE = 2 brushstrokes per minute
Similarly, Tom This can complete 60 brushstrokes in 60 minutes. So, Tom's RATE = 1 brushstroke per minute
So their, COMBINED rate = 2 + 1 = 3 brushstrokes per minute
How many minutes will it take them to paint the room working together?
Time = output/rate
So, time = 60/3 = 20 minutes
Answer: D
Cheers,
Brent
Retired Moderator
Joined: 16 Apr 2020
Status:Founder & Quant Trainer
Affiliations: Prepster Education
Posts: 1546
Given Kudos: 172
Location: India
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Re: If John can paint a room in 30 minutes and Tom can paint it
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03 Feb 2021, 08:03
03 Feb 2021, 08:03
1
If A can finish a job in X time period and B can finish the same job in Y time period, then A and B can together finish the same job in XY/(X+Y)
[Note: units for both the time periods must be same]
Using the same formula;
T = 30 x 60 / (30+60) = 1800/90 = 20 minutes
Hence, option D
[Note: units for both the time periods must be same]
Using the same formula;
T = 30 x 60 / (30+60) = 1800/90 = 20 minutes
Hence, option D
