Unit 5 - Normal Distrubution

Question 1

Normal distribution

Answer 1

• perfect symmetrical bell shaped curve (never touches horizontal axis)
• line of symmetry shows mean, median, mode of distribution
• wider the curve, larger the SD

Question 2

Standardised normal distribution

Answer 2

z = (x-μ)/ σ

z - probablitiy
x - score
μ - mean
σ - SD

• allows us to make comparisons

Question 3

How much % in SDs from the mean?

Answer 3

68% in 1 SD
95% in 2 SDs
99.7% in 3 SDs

Question 4

Normal distribution

Answer 4

N(mean, SD²)
ignore the ² I don’t know why its there/ what it means

Question 5

How to work out normal distribution?

Answer 5

1. Use the formula
2. Sketch the graph
3. Use the table
4. Compare with the graph (if you’re finding the left don’t do anything, if you’re finding the right, minus from 1)

Question 6

Double sided probabilities (in between)

Answer 6

Do it exactly the same but work out both z’s and subtract smaller from bigger at the end

Question 7

Working backwards

Answer 7

Sub into the formula and use the back table.
If finding under 50% find the reverse and put a - in the front → 25% would be -75%