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04 Feb 2022, 09:45
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Working at their respective, constant rates, Leslie can paint a fence in 2 hours and Darryl can paint the same fence in 4 hours. If they work together, how long will it take Leslie and Darryl to paint the fence?
A. 45 minutes
B. 1 hour, 20 minutes
C. 2 hours, 15 minutes
D. 3 hours
E. 6 hours
A. 45 minutes
B. 1 hour, 20 minutes
C. 2 hours, 15 minutes
D. 3 hours
E. 6 hours
04 Feb 2022, 10:33
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There is a formula for this you can memorize (T= AB/(A+B), but I recommend NOT doing that. It was the only thing I knew to do on the test, once, and as soon as a question deviated... I was hosed.
Instead there is a fundamental rule to remember whenever things are doing work together: **their individual rates can be added to their total rate**
So Leslie, if she paints the fence in 2 hours, works at a rate of 1/2 fences painted per hours. Darryl works 1/4 fences painted per hour. (this is from W=RT)
So together they paint 3/4 fences every hour.
That means they can paint a single fence in 4/3 hour
(again, W= RT:
1 = (3/4)*T
Solve for T: T = 4/3)
I know you could have just done AB/(A+B) here (2*4/(2+4) = 8/6 = 4/3)
But knowing how to work with different W=RT equations and add up individual rates for the 'combined' W = RT equation is a much broader skill for harder problems.
Instead there is a fundamental rule to remember whenever things are doing work together: **their individual rates can be added to their total rate**
So Leslie, if she paints the fence in 2 hours, works at a rate of 1/2 fences painted per hours. Darryl works 1/4 fences painted per hour. (this is from W=RT)
So together they paint 3/4 fences every hour.
That means they can paint a single fence in 4/3 hour
(again, W= RT:
1 = (3/4)*T
Solve for T: T = 4/3)
I know you could have just done AB/(A+B) here (2*4/(2+4) = 8/6 = 4/3)
But knowing how to work with different W=RT equations and add up individual rates for the 'combined' W = RT equation is a much broader skill for harder problems.
kungfury42
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04 Feb 2022, 14:00
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ReedArnoldMPREP
There is a formula for this you can memorize (T= AB/(A+B), but I recommend NOT doing that. It was the only thing I knew to do on the test, once, and as soon as a question deviated... I was hosed.
Instead there is a fundamental rule to remember whenever things are doing work together: **their individual rates can be added to their total rate**
So Leslie, if she paints the fence in 2 hours, works at a rate of 1/2 fences painted per hours. Darryl works 1/4 fences painted per hour. (this is from W=RT)
So together they paint 3/4 fences every hour.
That means they can paint a single fence in 4/3 hour
(again, W= RT:
1 = (3/4)*T
Solve for T: T = 4/3)
I know you could have just done AB/(A+B) here (2*4/(2+4) = 8/6 = 4/3)
But knowing how to work with different W=RT equations and add up individual rates for the 'combined' W = RT equation is a much broader skill for harder problems.
Instead there is a fundamental rule to remember whenever things are doing work together: **their individual rates can be added to their total rate**
So Leslie, if she paints the fence in 2 hours, works at a rate of 1/2 fences painted per hours. Darryl works 1/4 fences painted per hour. (this is from W=RT)
So together they paint 3/4 fences every hour.
That means they can paint a single fence in 4/3 hour
(again, W= RT:
1 = (3/4)*T
Solve for T: T = 4/3)
I know you could have just done AB/(A+B) here (2*4/(2+4) = 8/6 = 4/3)
But knowing how to work with different W=RT equations and add up individual rates for the 'combined' W = RT equation is a much broader skill for harder problems.
Hey can you please share the question you're talking about in the first paragraph, the one which deviated and left you hosed?
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