# Stats 1 - All you need to know

This was provided to me by my teacher, it's designed for the WJEC stats 1 syllabus. It doesn't go over everything but it just goes through the basic things that you need to remember :)

- Created by: lava-mite
- Created on: 20-04-12 13:14

First 312 words of the document:

ALL YOU NEED TO KNOW- WJEC STATISTICS 1

PROBABILITY

1. Simple Probability

Remember OR is + AND is ×

n

2. Cr

When 3 are selected from a group containing different types.

Example: If 2 red, 3 blue and 4 yellow, select 3.

2

C1 3 C1 4 C1

P(one of each colour) = 9

C3

3

C3 4C3

P(3 same colour) = P(3 blue) +P(3 yellow) = 9

C3

2

C 2 7 C1

P(2 reds are selected) = 9

C3

5

C3

P(at least 1 yellow) = 1 P(no yellows) = 1- 9

C3

3. Union and intersection (Venn diagram)

Union = A or B or both (total)

Intersection = Both A and B (overlap)

A/ is "not A"

P(AUB) = P(A)+P(B)-P(AB)

If mutually exclusive P(AB)=0

If independent P(AB) = P(A) × P(B)

Conditional probability: P(B|A) =P(AB)

P(A)

4. Tree Diagrams

Will be given probability of one event dependent on another.

a) Find a probability by multiplying along branches and adding.

b) Will be conditional probability

c) A second item or test may be taken, draw a third set of branches.

d) Find probability that the second item gives a certain outcome, use

conditional probability.

5. Discrete random variables

Usually given a table, but if given a formula make own table.

If probabilities given in terms of k, then use the total = 1 to find k.

Mean E(X) = xP(X=x)

E(X2) = x2 P(X=x)

Variance = E(X2) E(X)2 standard deviation = variance

1 1

E( ) P(X x)

X x

If X1 and X2 are 2 independent occurrences find P(X1 + X2 = 4), find all

options of making total of 4 remember the order is important, 1-3, 2-2, 3-1.

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