Question 1135838
A new type of pump can drain a certain pool in 4
 hours. An older pump can drain the pool in 
6 hours. How long will it take both pumps working together to drain the pool?
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There's a shortcut for problems like this:
4*6/(4+6) = 2.4 hours
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Greenstamps' method is similar, but I wouldn't bother with the LCM, just use the product, 6*4 = 24.  Same result.
Teachers and texts seem to be obsessed with LEAST common multiple, for no good reason.  Just wastes your time.