Stats GCSE Probability Distributions
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26 Terms
1
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What is a probability distribution?
A list of all the possible outcomes together with their probabilities
2
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What are the conditions for BD?
There’s fixed number of trials
Each trial has 2 outcomes
All the trials are independent of each other
Probabilities are fixed
Each trial has 2 outcomes
All the trials are independent of each other
Probabilities are fixed
3
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What do p&q stand for in BD?
p-probability of success
q-probability of failure
q-probability of failure
4
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How to find probabilities in BD
Identify the 2 outcomes and find their probabilities
Expand (p+q)^n, leaving p and q as letters
Find the terms that has p to the power of x successes
Substitute values of p and q, then calculate
Expand (p+q)^n, leaving p and q as letters
Find the terms that has p to the power of x successes
Substitute values of p and q, then calculate
5
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How to show BD
B(n,p)
6
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What’s the mean of BD?
np (number of trials\*probability of success)
7
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Calculator shortcut for BD
Find the coefficient by using nCr (n is trials and r is successes)
8
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How to show ND
N(μ,σ^2)
9
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What does μ and σ^2 stand for in ND?
μ-mean
σ^2- variance
σ^2- variance
10
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What does ND look like?
Smooth bell shaped curve
11
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What are the conditions for ND
the data is continuous
the distribution is symmetrical
the mode, median, and mean are about the same
the distribution is symmetrical
the mode, median, and mean are about the same
12
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What kind of data works for ND?
Heights, weights, time
13
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What is ND not suitable for?
Skewed data
14
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What percentage of the data lies within 1sd of the mean?
68%
15
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What percentage of the data lies between 2sd of the mean?
95%
16
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What percentage of the data lies within 3sd of the mean?
99\.8%
17
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What are standardised scores used for?
Comparing how far above or below average individual values are
18
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How to calculate standardised score
(score-mean)/standard deviation
19
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How to interpret standardised score
positive-score>mean
negative-score
negative-score
20
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What is quality assurance?
Checking samples to make sure products are of good quality
21
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What is a control chart?
Time series chart used for quality assurance
22
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What are the 5 lines on a control chart for?
middle line-target value
inner two lines-upper and lower warning limits
outer two lines-upper and lower action limits
inner two lines-upper and lower warning limits
outer two lines-upper and lower action limits
23
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What are the warning limits on a control chart?
2sd above/below target value
24
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What do you do if a sample is outside the warning limits?
Take another sample to see if there is a problem, and if so production is stopped
25
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What are the action limits on a control chart?
3sd above/below target value
26
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What do you do is a sample is outside action limits?
Stop production immediately
Note 
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