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January 29, 2009

Man and dog problem



A man is taking his dog for a walk. They set off together for a
waterfall 10 miles away. They set off exactly together and the
man walks at a steady 4 miles an hour. The dog runs off at 8 miles
an hour and when it reaches the waterfall it turns round and
runs back to the man. When it reaches the man it turns round and
runs back to the waterfall and so on until the man and dog arrive
at the waterfall. when they both arrive at waterfall ?

4 comments:

Anonymous said...

The time taken is 50 minutes.

time=10 miles * 60 minutes/ ( 4 + 8 ) miles per 60 minutes=50 minutes.

Secret Squïrrel said...

Ignore the dog. If the man walks at 4mph it will take him 2.5 hrs to walk the 10 miles.

Pradheep said...

Ya they take 2:30 Hrs to reach since the man will only reach at that time only no matter the dog runs or flies.

ayush said...

A better question would be, how much did the dog travel?
at first you might get confused, but if you think clearly then dog is basically running at his speed for the amount of time man takes to reach waterfall(i.e.) 2.5 hrs. So, distance travelled by dog = 8*2.5=20 miles.