Posted by diane on Thursday, April 9, 2009 at 9:38am.
it takes bill 4 hours to paint a house. it takes john 7 hours to paint the same house. how long does it take to paint the house if they painted it together.

math  Lu, Thursday, April 9, 2009 at 10:07am
7+4= 11/2 is equal to 9 and 1 half hours.

math  Damon, Thursday, April 9, 2009 at 11:22am
Oh heavens, it takes them longer working together Lu ????
Bill paints 1/4 house per hour
John paints 1/7 house per hour
so together they paint
1/4 + 1/ 7 = 7/28 + 4/28 = 11/28 houses per hour
which is 28 /11 hours/house
or around 2.55 hours
or 2 hours and 33 minutes
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