Question

I know this is a really simple question, but I ALWAYS forget the formula for this type of question...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?

Answer 1

don't know about formula, but sally can paint 1/4 of house in hour, and john can paint 1/6, so together in one hour they can paint 5 / 12 of house in hour, so it takes 12/5 hours

Answer 2

(= 2.4 hours)

Answer 3

if you do more than one or two of these, you see that the answer will be
\[\frac{4\times 6}{4+6}\]

Answer 4

Whoa! All the time satellite?

Answer 5

And thank you blahx3!

Answer 6

not that i suggest you remember this "formula" you can always reason it out as blah did. in fact if the question said "how long would it take to paint 3/4 of the house?" this simple trick would not work