Question 1205975
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Consider the area to clean is 210 square feet.
I'm getting this value from the fact 7*3 = 21 is the LCM of the given values. 
Then I tacked on a 0 at the end to make the square footage more realistic. 
This is just an example value. Feel free to pick another.


Josh cleans 210 sq ft in 3 hours when working alone.
His unit rate is 210/3 = 70 sq ft per hour.


Ken cleans 210 sq ft in 7 hours when working alone.
His unit rate is 210/7 = 30 sq ft per hour.


Add the unit rates: 70+30 = 100 
If the two men work together, without either person getting in the way of the other, then their combined unit rate is 100 sq ft per hour.


When working together it will take 210/100 = <font color=red>2.1 hours</font>.


If you wanted the answer in minutes only, then,
2.1 hrs = 2.1*60 
2.1 hrs = <font color=red>126 min</font>


Or if you wanted hrs+min format, 
126 min = 120 min + 6 min
126 min = <font color=red>2 hr + 6 min</font>
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