Re: Word problem
These are trivial if you have seen them and remember how to do them - just like most other things.
Think about UNITS of time. We have a four hour and a six hour. How can those be added and have the answer make sense? The answer is in a common unit.
"Sally can paint a house in 4 hours" ==> Sally can paint 1/4 of a house in one (1) hour.
"John can paint a house in 6 hours" ==> John can paint 1/6 of a house in one (1) hour.
Notice how each translation was performed merely by finding the reciprocal of the given information. hours / house {flip} houses/hour
This is much more useful information as 1/4 + 1/6 = 3/12 + 2/12 = 5/12 and working together they can paint 5/12 of a house in one (1) hour.
Translating back, using the reciprocal again, "5/12 of a house in one (1) hour" ==> One (1) house can be painted in 12/5 hours.
From a practical point of view, just filp everything upside-down.
1/4 + 1/6 = 1/x and solve for 'x'.
Note: This problem assumes Sally and John work together PERFECTLY. They cannot trip over each other. They can't take each others' brushes or paint cans or ladders. If John is feeling a little distracted and finds himself staring dreamily at Sally, that certainly could slow things down. :shock: Anyway, normally it would be expected to assume they do not interfere with each other.
