Not to say that you're wrong... but the Bingo I played years ago had a board with 25 numbers on it (5 columns with 5 numbers each). The columns were labeled B, I, N, G, and O. And there were 75 possible numbers, not 90.

Another restriction is that each column on your board was restricted to a set of 15 numbers... So, in the B column, you could only have numbers 1-15, I column, 16-30, etc. Therefore, the number of possible bingo cards is not 75c25, but rather 15c5 * 5 (for blackout purposes)... for non-blackout purposes, you'd have 15p5 * 5.

This is what I remember, anyway... I'm no bingo expert, and the game undoubtedly has tons of variations.