An airplane flying at 500 miles an hour leaves Minneapolis O

An airplane flying at 500 miles an hour leaves Minneapolis. One-half hour later, a second airplane leaves Minneapolis flying in the same direction at rate of 600 miles per hour. How long will it take the second airplane to overtake the first?

Solution

There\'s a hard way to do these, but take the easy way:
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In 1/2 hour, the 1st plane is 250 miles away (500*0.5)
The 2nd plane gains in it at 100 mph (600-500)
250/100 = 2.5 hours.