Calculate probabilities in bingo

combinatoricsprobability

All cards have 5 columns and 3 rows (15 numbers) and we have 60 numbers in total but the extraction have 30 numbers.

I'm trying to solve a bingo problem that is : Determine the probability of hitting the first row (all 5 numbers) and not hitting the first and last column (at least one of that 4 numbers,because two of them hit in the first row, don't hit).

So i used combinations.
I try this way :
$$ \frac {{{5}\choose{5}}*{{25}\choose{10}}-4*{{21}\choose{6}}}{{60}\choose{30}} $$
where
$$ {25}\choose{10} $$
is the possibilities of put the 10 missing numbers on the card and
$$ 4*{{21}\choose{6}}$$
because we don't want to hit 1 of the 4 numbers of the first and last column and the last numbers could be anyone.

I need change something or is this right ?
Thanks 🙂

Best Answer

The probability $P(A)$ of hitting the first row (all 5 numbers) is $$P(A)=\frac{\binom{55}{25}}{\binom{60}{30}}$$ Given $A$, the probability $P(B)$ of hitting the other 4 numbers in the first and last columns is $$P(B)=\frac{\binom{51}{21}}{\binom{55}{25}}$$ You want $P(A)\times(1-P(B))$ $$\frac{\binom{55}{25}}{\binom{60}{30}}\times\frac{\binom{55}{25}-\binom{51}{21}}{\binom{55}{25}}=\frac{\binom{55}{25}-\binom{51}{21}}{\binom{60}{30}}$$

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