probabilty of choosing squares in diagonal

• Jan 8th 2009, 02:04 AM
kannan
probabilty of choosing squares in diagonal
Hello ,
This my first post here.

Two blocks are chosen randomly on a chess board. What is the probability that they lie on the same diagonal?

2 blocks can be chosen in 64C2 ways .
now we have to choose 2 blocks that lie in the same diagonal.
this can be done in 2 x 8C2 ways (as there are 2 diagonals)
so the probability is 56/2016. this is wrong according to the book.
Thank you
• Jan 8th 2009, 02:30 AM
Isomorphism
Quote:

Originally Posted by kannan
Hello ,
This my first post here.

Two blocks are chosen randomly on a chess board. What is the probability that they lie on the same diagonal?

Are you sure they are talking only about the main diagonal? (Wink)
• Jan 8th 2009, 06:46 AM
kannan
Quote:

Originally Posted by Isomorphism
Are you sure they are talking only about the main diagonal? (Wink)

oh i must have gone wrong there and is this answer right if they are talking about the main diagonal?
Thank you very much
• Jan 8th 2009, 08:16 AM
Plato
Quote:

Originally Posted by kannan
oh i must have gone wrong there and is this answer right if they are talking about the main diagonal?

Yes for the 'main diagonal' that is correct.