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12-107.

Hospital records show that $10\%$ of all the cases of a certain disease are fatal. If five patients suffer from this disease, find the probability that: Homework Help ✎

1. All will recover.

If $10\%$ die, what percentage recover?

Another way to think of this is that none of the patients die.

$_5C_0(0.9)^5(0.1)^0$

1. At least three will die.

Add up the probabilities that $3$ die, $4$ die, and $5$ die.

The probability that $3$ die is

$_5C_3(0.9)^2(0.1)^3.$