Question 479081
Four men take 3 hours to paint a wall. How much time would 6 men take to do the same job? (Ans. 2 Hours)
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Do it in your head:

The least common multiple of 4 men and 6 men is 12 men.

>>Four men take 3 hours to paint a wall,...<<

12 men is 3 times as many men as 4 men, so they can paint the wall
3 times as fast, which means they can paint it in only 1 hour.

Now 6 men is only half as many men as 12 men, so it takes them twice 
as long as it takes 12 men.  So it takes 6 men 2 hours.

Edwin</pre>