Tag Archives: classic puzzle

Two Gems


I would like to share following two mathematical problems which were brought to my knowledge by different people.

  • Boy or Girl Paradox by Guru boy-girl-paradox

Statement of the problem is:

X has two children.  Find the probability that:

  •  Both children are girls, given that the older child is a girl.

  • Both children are boys, given that at least one of them is a boy.

Some historical reference can be found at Wikipedia: http://en.wikipedia.org/wiki/Boy_or_Girl_paradox

Also you can refer to this interesting paper published on this problem by Peter Lynch : http://mathsci.ucd.ie/~plynch/Publications/BIMS-TwoChildParadox.pdf 

  • The twelve-coin problem by Sagar Shrivastava


Statement of the problem is:

There is a pile of twelve coins, all of equal size. Eleven are of equal weight. One is of a different weight. What are minimum number of times one need to weigh to find the faulty coin and determine if it is heavier or lighter?

Some historical reference can be found at this wikipedia page: http://en.wikipedia.org/wiki/Balance_puzzle

Also, a discussion on this problem is available at: http://mathforum.org/library/drmath/view/55618.html

Golden Year Puzzle


This is a puzzle proposed by D. R. Kaprekar in year1984.

In the year 1949, a man turned 67. His four sons turned 37, 31, 29, 23. All the five reached prime age in a prime year. It was the golden year for the family. When was or will be their next golden year ?

(Prob 8-3-1, Function, Col 8, Dept of Mathematics, Monash University, Claighton, Victoria, 3168, July 84, pg. 28)