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December 21, 2014

December 21, 2014

Posted by **muffy** on Saturday, September 12, 2009 at 12:31pm.

Please let me know if I am correct.

First I took the average of 4 and 7 and got 5.5 hours. So they can both paint the room in 5.5 hours.

Next, If they start at 9:30 they will finish at 3:00

Next if they have to leave 45 minutes early to get to a 12:00 show, they should leave at 11:15.

Next, therefore, they will be 3:45 minutes late for the 12:00 show.

- math -
**bobpursley**, Saturday, September 12, 2009 at 12:47pmYou cant trust the average always.

I assume you are using a rate equation,

amount=rate*time

Consider in 28 hours, shelby can paint 7, and Zoe can paint 4. So the combined rate = (7+4 rooms)/28 hrs= 11/28 rooms/hr

Now the time to paint one room

amount= rate*time

time= amount/rate= 1room/(11/28 room/hr)

time= 1*28/11 hrs= 2.54hrs= 2hrs 33min

If they start at 9:30, then they finish about three min after noon. Check my thinking and calculations.

Now on your thinking... Using the average 5.5hrs per room, but BOTH are working, that is the average for each, so time for both together would be 5.5/2= 2.75hrs, which is not 28/11 hrs (2.545hrs). SO dont use the average, throw away that thinking, it wont work.

- math -
**muffy**, Saturday, September 12, 2009 at 1:26pmThank you soooooooo much, you are a great teacher! I truly understand!

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