Question 1194803
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Let's say that the task is to move 80 boxes.


Peter needs 8 hours to do the task on his own. 
His unit rate is 80/8 = 10 boxes per hour.


Sam works twice as fast as Peter, meaning his unit rate is 2*10 = 20 boxes per hour when Sam works alone.


If the two men work together, without hindering one another, then their combined unit rate is 10+20 = 30 boxes per hour.


x = number of hours needed to complete the task if the two men work together


(rate)*(time) = amount done
(30 boxes per hour)*(x hours) = 80 boxes total
30x = 80
x = 80/30
x = 8/3
x = (6+2)/3
x = 6/3+2/3
x = 2+2/3
x = 2 & 2/3


Answer as an improper fraction: 8/3 hours
Answer as an mixed number: 2 & 2/3 hours
Answer as a decimal: 2.67 hours approximately


Side note: 2/3 hour = (2/3)*60 = 40 minutes
Meaning that 8/3 hr = 2 & 2/3 hr = 2 hr + 40 min
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