Puzzle 36 - Solution

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 I will give you the solution of bonus question first. 

The answer is infinite speed

Question was :

  Tom wants to travel from San Francisco to  Los Angeles and back - a round trip -  with an average speed of 50 mph. If you are feeling very patriotic change the name of the person to Suresh and cities to Delhi and Agra. 

Due to traffic, he could travel only at 25 mph on the way to Los Angeles. What must be his speed on return journey in order to get an average speed of 50 mph.

Here is  why

Let us distance between the two cities is x.

  •  So Tom wants to travel the round trip in - 2x/50 hours - the distance being 2x = x/25 hours . The total time = x/25
  • Now for onward journey he has taken x/25 hours - x miles with the speed of 25 mph.
  • So which means he has to cover the rest of the distance - x miles in a time of total time - x/25 = x/25 - x/25 = 0 hours
  • The speed needed will be x/0 = infinite. 

And the other question was 

How do we get 10 using 1,1, 5 and 8 using all of these and any operators.

 The solution is

      8/(1 - 1/5) 

  = 8/(4/5) = 8X5 / 4 = 40/4 = 10

The delay in publishing the answer was due to the difficulty of searching for the solution online

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