Question 1195305
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1 and a half = 1 + 1/2 = 1.5
2 and a half = 2 + 1/2 = 2.5


1.5*2.5 = 3.75


Let's say there are 375 plants of lettuce. 
I'm picking this number so that the division results of the next two paragraphs are whole numbers. 
The number is derived from moving the decimal point on 3.75 two spots to the right to arrive at 375.


Brown can plant all that lettuce in 1.5 hours if he works alone. 
His unit rate is 375/(1.5) = 250 plants per hour. 
The unit rate is found by dividing the number of plants over the time needed.
Think of the formula distance = rate*time which rearranges into rate = distance/time. 
In this case, "distance" is the amount done, aka the amount planted.


The son can do the same job, when working alone, in 2.5 hours. The son's unit rate is 375/(2.5) = 150 plants per hour.


If the two work together without getting in each other's way, then their combined unit rate is 250+150 = 400 plants per hour.


x = number of hours they work together
400x = amount planted
400x = 375
x = 375/400
x = (15*25)/(16*25)
x = 15/16
x = 0.9375


Answer as a fraction = 15/16 of an hour
Answer as a decimal = 0.9375 of an hour


If you wanted to convert to minutes, then,
0.9375 hrs = 0.9375*60 = 56.25 min
which further breaks down into
56.25 min = 56 min + 15 sec
because 15 seconds is 15/60 = 1/4 = 0.25 of a minute
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