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## Homework Statement

let x be a random variable with

P(X=-1) = 1/4

P(X=0) = 1/4

P(X=1) = 1/2

Let S be the sum of 25 independant random variables each with the same distribution as X.

Calculate approximately

a) P(S<0)

b) P(S=0)

c) P(S>0)

## Homework Equations

Quite possibly the normal approximation.

## The Attempt at a Solution

I'm not sure how to start this at all. Please help.

The answers are

a) P(S<0) = 0.05

b) P(S=0) = 0.03

c) P(S>0) = 0.92

Thanks in advanced!