Question 233246
2. If Sally can paint a house in 4 hours, and John can paint the same house in 6 hour, 
how long will it take for both of them to paint the house together?
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Here's an easy method to do these "shared work" problems 
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Let t = time required when they work together
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Let the completed job = 1; (a painted house in this case)
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Each person will do a fraction of the work, the two fractions add up to 1
{{{t/4}}} + {{{t/6}}} = 1
multiply equation by 12 to get rid of the denominators, results:
3t + 2t = 12
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5t = 12
t = {{{12/5}}}
t = 2.4 hrs working together
Convert .4 hrs to min: .4 * 60 = 24 min
t = 2 hr 24 min
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You can prove this to yourself:
{{{2.4/4}}} + {{{2.4/6}}} = 
.6 + .4 = 1
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Wasn't that pretty easy to understand??