In a standard set of dominoes, a face of each domino has a line through the center, with 0 to 6 dots on each side of the line. Each possible combination of dots is used exactly once, one combination per domino. What is the probability that a randomly selected domino will have the same number of dots on both sides of the line? Express your answer as a common fraction.
I thought the answer was 1/7 did I make a mistake?
Yes, you made a mistake.
There are 7 dominoes out of 28 that have the same number on each side of the line.
Simplify 7/28
How do you know there are 28 dominoes?
It doesn't say in the question. So is it expecting us to know that a standard set has 28 dominoes?
I Googled.
http://www.google.com/#q=standard+set+of+dominoes