# Math Help - Spider Probability Problem

1. ## Spider Probability Problem

A spider eats 3 flies a day. Until the spider fills its quota, it has an equal chance of catching any fly that attempts to pass. A fly is about to make an attempt. What is the chance of survival given that 5 flies have already made the attempt today?

2. Originally Posted by sweeetcaroline
A spider eats 3 flies a day. Until the spider fills its quota, it has an equal chance of catching any fly that attempts to pass. A fly is about to make an attempt. What is the chance of survival given that 5 flies have already made the attempt today?
Pr(survival) $= \Pr(X = 3) \cdot 0 + \Pr(X < 3) \cdot \frac{1}{2}$.

Use the fact that X ~ Binomial(n = 5, p = 1/2) to calculate $\Pr(X < 3)$.