Aug 042017
 

You may solve the simple probability, “Given a set of n randomly chosen people, what is the probability of two people having same birthday?”

You may also solve,  “At least how many people need to be picked to make the probability 100% that at least two of them have same birthday?”

Answer to the second question is 367, because there are 366 possible birthdays (including Feb-26).

The question now is, “At least how many people need to be picked to make the probability 99.9% that at least two of them have same birthday?”

Answer is 70.

And if the question is,“At least how many people need to be picked to make the probability 50% that at least two of them have same birthday?”

Answer is 23.

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Sep 242015
 

Four glasses are placed on the four corners of a square rotating table. Each glass is either upright (up) or upside-down (down). You have to turn all the glasses in same direction (either all up or all down). There are following conditions

  1. You are blindfolded,
  2. At one time you can only change two glasses (and you cannot touch other two glasses).
  3. The table spins after each time you change the glasses.

When all the glasses comes in one direction, then a bell rings and the game stops?
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Jun 132012
 

Two friends decided to get together and start riding bikes towards each other, both at a speed of 6 km/hr (starting at the same time). The live 36 km apart and hence will meet halfway.

One of them have a pet pigeon and it starts flying the instant the friends start traveling. The pigeon flies back and forth between the two friends, at a speed of 18 km/hr until the friends meet.

How much distance (in km) will the pigeon travel? Continue reading »