Question 1002869
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Let's say for a hypothetical argument that each chair's surface area is 900 square inches.
As it turns out, this figure 900 doesn't matter since you can change it to any positive real number you want. The final answer at the end will remain the same.



Kimberly can paint one chair (900 square inches) in 45 minutes, so her unit rate is 20 square inches per minute because:
rate = amountDone/time = 900/45 = 20 square inches per minute



Meanwhile,
Arthur's unit rate = 900/30 = 30 square inches per minute


When the two work together, the combined unit rate would be 20+30 = 50 square inches per minute. 
This assumes neither person slows the other down.


1 chair has 900 square inches of material.
6 chairs cover 6*900 = 5400 square inches


rate*time = amountDone
time = amountDone/rate
time = 5400/50
time = 108 minutes
time = 60 min + 48 min
time = 1 hr + 48 min



Answer: <font color=red>108 minutes</font> (i.e. <font color=red>1 hour & 48 minutes</font>)


Side note: The answer by mananth applies to 1 chair. You have to multiply 18 by 6 to get the time duration for 6 chairs.
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