math
posted by diane .
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.

7+4= 11/2 is equal to 9 and 1 half hours.

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