// Numbas version: finer_feedback_settings {"name": "PB1 - Joint Probability", "extensions": [], "custom_part_types": [], "resources": [], "navigation": {"allowregen": true, "showfrontpage": false, "preventleave": false, "typeendtoleave": false}, "question_groups": [{"pickingStrategy": "all-ordered", "questions": [{"name": "PB1 - Joint Probability", "tags": [], "metadata": {"description": "", "licence": "Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International"}, "statement": "

Researchers collected observations of bee species and recorded if the bee size was tiny (t) or large (l), and whether the bee was a red-tailed bumblebee (r) or a red-shanked carder bumblebee (c).

\n

These two discrete variables were not independent.

\n

This data was used to make this joint probability table:

\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Bee=red-tailed bumblebee ($B=r$)Bee=red-shanked carder bumblebee ($B=c$)
Size = tiny ($S=t$){rttext}{cttext}
Size = large ($S=l$){rltext}{cltext}
", "advice": "

a) We have been asked to find the joint probability for a bee that is {jointpdfchoice}.

\n

We can read this off of the table as {notation}={jointpdftext}.

\n

b) To calculate the marginal probability of the bee being {size}, we must find {sizenotation}.

\n

\\begin{align}
\\var{sizenotation} &= \\var{sizesumnotation} \\\\
&= \\var{sizeprob}.
\\end{align}

\n

c) To calculate the marginal probability of the bee being a {bee} bumblee, we must find {beenotation}.

\n

\\begin{align}
\\var{beenotation} &= \\var{beesumnotation} \\\\
&= \\var{beeprob}.
\\end{align}

\n

d) For the conditional probability we want to know what is the probability that it is a {beecond} bumblee given the bee is {sizecond}. We must find {condnotation}.

\n

\\begin{align}
\\var{condnotation} &= \\var{condformula} \\\\
&= \\frac{\\var{condnum}}{\\var{conddenom}} \\\\
&= \\var{condprob}.
\\end{align}

\n

e) We are asked to calculate \\var{condnotation2}.

\n

We can use our previous answer to help us calculate this conditional probability since, 

\n

\\begin{align}
\\var{condnotation2} + \\var{condnotation} &= \\var{condformula} + \\var{cond2formula} \\\\
&= \\frac{\\var{condformula_advice}}{\\var{condformula_advice}} \\\\
&= 1.
\\end{align}

\n

So, $\\var{condnotation2} = 1 - \\var{condnotation}$.

\n

Hence, 

\n

\\begin{align}
\\var{condnotation2} &= 1 - \\var{condnotation} \\\\
&= 1 - \\var{condprob} \\\\
&= \\var{1-condprob}.
\\end{align}

\n

f) To demonstrate that two random variables, $B$ and $S$, are not independent, you can show that their joint probability distribution is not equal to the product of their individual (marginal) probability distributions.

\n

\n

Use this link to find some resources which will help you revise this topic.

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Which value are we asking the students to read off the table

", "templateType": "anything", "can_override": false}, "jointpdfchoice": {"name": "jointpdfchoice", "group": "Read off table - joint probability", "definition": "if(random1=1,'tiny and a red-tailed',if(random1=2,'tiny and a red-shanked carder',if(random1=3,'large and a red-tailed',if(random1=4,'large and a red-shanked carder',0))))", "description": "

Text for which probability we're asking the students to read off the table

", "templateType": "anything", "can_override": false}, "jointpdf": {"name": "jointpdf", "group": "Read off table - joint probability", "definition": "if(random1=1,rt,if(random1=2,ct,if(random1=3,rl,if(random1=4,cl,0))))", "description": "

joint probability 

", "templateType": "anything", "can_override": false}, "notation": {"name": "notation", "group": "Read off table - joint probability", "definition": "if(random1=1,'$P(S=t, B=r)$',if(random1=2,'$P(S=t, B=c)$',if(random1=3,'$P(S=l, B=r)$',if(random1=4,'$P(S=l, B=c)$',0))))", "description": "

Notation for selected joint probability 

", "templateType": "anything", "can_override": false}, "random2": {"name": "random2", "group": "marginal probability", "definition": "random(0,0,1,1)", "description": "

Random number to decide whicih size we want the marginal probability for

", "templateType": "anything", "can_override": false}, "size": {"name": "size", "group": "marginal probability", "definition": "if(random2=0,'tiny',if(random2=1,'large',0))", "description": "

text for which size we want the marginal probability for 

", "templateType": "anything", "can_override": false}, "sizeprob": {"name": "sizeprob", "group": "marginal probability", "definition": "if(random2=0,rt+ct,if(random2=1,rl+cl,0))", "description": "

marginal probability for sleected bee size

", "templateType": "anything", "can_override": false}, "sizenotation": {"name": "sizenotation", "group": "marginal probability", "definition": "if(random2=0,'$P(S=t)$',if(random2=1,'$P(S=l)$',0))", "description": "

mathematical notation for marginal probability of selected bee size

", "templateType": "anything", "can_override": false}, "bee": {"name": "bee", "group": "marginal probability", "definition": "if(random2=0,'red-tailed',if(random2=1,'red-shanked carder',0))", "description": "

The bee type we want the marginal probability for

", "templateType": "anything", "can_override": false}, "beeprob": {"name": "beeprob", "group": "marginal probability", "definition": "if(random2=0,rt+rl,if(random2=1,ct+cl,0))", "description": "

The marginal probability of the selected bee type

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The notation for the marginal probaility of the selected bee type

", "templateType": "anything", "can_override": false}, "rttext0": {"name": "rttext0", "group": "probabilities set 0", "definition": "\"

$\\\\frac{2}{12}$

\"", "description": "

text for table

", "templateType": "long string", "can_override": false}, "cttext0": {"name": "cttext0", "group": "probabilities set 0", "definition": "\"

$\\\\frac{3}{12}$

\"", "description": "

text for table

", "templateType": "long string", "can_override": false}, "rltext0": {"name": "rltext0", "group": "probabilities set 0", "definition": "\"

$\\\\frac{6}{12}$

\"", "description": "

text for table

", "templateType": "long string", "can_override": false}, "cltext0": {"name": "cltext0", "group": "probabilities set 0", "definition": "\"

$\\\\frac{1}{12}$

\"", "description": "

text for table

", "templateType": "long string", "can_override": false}, "cttext": {"name": "cttext", "group": "Ungrouped variables", "definition": "if(random=0,cttext0,if(random=1,cttext1,0))", "description": "", "templateType": "anything", "can_override": false}, "rttext": {"name": "rttext", "group": "Ungrouped variables", "definition": "if(random=0,rttext0,if(random=1,rttext1,0))", "description": "

text for table

", "templateType": "anything", "can_override": false}, "cltext": {"name": "cltext", "group": "Ungrouped variables", "definition": "if(random=0,cltext0,if(random=1,cltext1,0))", "description": "

text for table

", "templateType": "anything", "can_override": false}, "rltext": {"name": "rltext", "group": "Ungrouped variables", "definition": "if(random=0,rltext0,if(random=1,rltext1,0))", "description": "

text for table

", "templateType": "anything", "can_override": false}, "random3a": {"name": "random3a", "group": "Conditional Probability", "definition": "random(0,0,1,1)", "description": "", "templateType": "anything", "can_override": false}, "sizecond": {"name": "sizecond", "group": "Conditional Probability", "definition": "if(random3a=0, 'tiny',if(random3a=1,'large',0))", "description": "

size of bee for conditional probability

", "templateType": "anything", "can_override": false}, "beecond": {"name": "beecond", "group": "Conditional Probability", "definition": "if(random3b=1, 'red-tailed', if(random3b=0, 'red-shanked carder',0))", "description": "

bee type for conditional probability

", "templateType": "anything", "can_override": false}, "random3b": {"name": "random3b", "group": "Conditional Probability", "definition": "random(0,0,1,1)", "description": "", "templateType": "anything", "can_override": false}, "condnotation": {"name": "condnotation", "group": "Conditional Probability", "definition": "if(random3a=0 and random3b=0, '$P(B=c|S=t)$',if(random3a=1 and random3b=0, '$P(B=c|S=l)$',if(random3a=0 and random3b=1, '$P(B=r|S=t)$',if(random3a=1 and random3b=1, '$P(B=r|S=l)$',0))))", "description": "

mathematical notation for selected conditional probability

", "templateType": "anything", "can_override": false}, "condprob": {"name": "condprob", "group": "Conditional Probability", "definition": "if(random3a=0 and random3b=0, ct/(rt+ct), if(random3a=1 and random3b=0, cl/(rl+cl), if(random3a=0 and random3b=1, rt/(rt+ct), if(random3a=1 and random3b=1, rl/(rl+cl),0))))", "description": "

calculated condition probability for sleected bee size and type

", "templateType": "anything", "can_override": false}, "condnotation2": {"name": "condnotation2", "group": "Conditional Probability", "definition": "if(random3a=0 and random3b=0, '$P(B=r|S=t)$',if(random3a=1 and random3b=0, '$P(B=r|S=l)$',if(random3a=0 and random3b=1, '$P(B=c|S=t)$',if(random3a=1 and random3b=1, '$P(B=c|S=l)$',0))))", "description": "

Complimentary conditional probability notation so we can check they sum to one

", "templateType": "anything", "can_override": false}, "rt1": {"name": "rt1", "group": "probabilities set 1", "definition": "3/18", "description": "

joint probability

", "templateType": "anything", "can_override": false}, "ct1": {"name": "ct1", "group": "probabilities set 1", "definition": "5/18", "description": "

joint probability

", "templateType": "anything", "can_override": false}, "rl1": {"name": "rl1", "group": "probabilities set 1", "definition": "4/18", "description": "

joint probability

", "templateType": "anything", "can_override": false}, "cl1": {"name": "cl1", "group": "probabilities set 1", "definition": "6/18", "description": "

joint probability

", "templateType": "anything", "can_override": false}, "rttext1": {"name": "rttext1", "group": "probabilities set 1", "definition": "\"

$\\\\frac{3}{18}$

\"", "description": "

text for table

", "templateType": "long string", "can_override": false}, "cttext1": {"name": "cttext1", "group": "probabilities set 1", "definition": "\"

$\\\\frac{5}{18}$

\"", "description": "

text for table

", "templateType": "long string", "can_override": false}, "rltext1": {"name": "rltext1", "group": "probabilities set 1", "definition": "safe(\"

$\\\\frac{4}{18}$

\")", "description": "

text for table

", "templateType": "long string", "can_override": false}, "cltext1": {"name": "cltext1", "group": "probabilities set 1", "definition": "\"

$\\\\frac{6}{18}$

\"", "description": "

text for table

", "templateType": "long string", "can_override": false}, "jointpdftext": {"name": "jointpdftext", "group": "Read off table - joint probability", "definition": "if(random1=1,rttext,if(random1=2,cttext,if(random1=3,rltext,if(random1=4,cltext,0))))", "description": "", "templateType": "anything", "can_override": false}, "sizesumnotation": {"name": "sizesumnotation", "group": "marginal probability", "definition": "if(random2=0,'$P(S=t,B=r)+P(S=t,B=c)$',if(random2=1,'$P(S=l,B=r)+P(S=l,B=c)$',0))", "description": "", "templateType": "anything", "can_override": false}, "beesumnotation": {"name": "beesumnotation", "group": "marginal probability", "definition": "if(random2=0,'$P(S=t,B=r)+P(S=l,B=r)$',if(random2=1,'$P(S=t,B=c)+P(S=l,B=c)$',0))", "description": "", "templateType": "anything", "can_override": false}, "condformula": {"name": "condformula", "group": "Conditional Probability", "definition": "if(random3a=0 and random3b=0, '$P(B=c,S=t)/P(S=t)$',if(random3a=1 and random3b=0, '$P(B=c,S=l)/P(S=l)$',if(random3a=0 and random3b=1, '$P(B=r,S=t)/P(S=t)$',if(random3a=1 and random3b=1, '$P(B=r,S=l)/P(S=l)$',0))))", "description": "", "templateType": "anything", "can_override": false}, "condnum": {"name": "condnum", "group": "Conditional Probability", "definition": "if(random3a=0 and random3b=0, ct, if(random3a=1 and random3b=0, cl, if(random3a=0 and random3b=1, rt, if(random3a=1 and random3b=1, rl,0))))", "description": "", "templateType": "anything", "can_override": false}, "conddenom": {"name": "conddenom", "group": "Conditional Probability", "definition": "if(random3a=0, rt+ct, if(random3a=1, rl+cl, 0))", "description": "", "templateType": "anything", "can_override": false}, "cond2formula": {"name": "cond2formula", "group": "Conditional Probability", "definition": "if(random3a=0 and random3b=0, '$P(B=r|S=t)/P(S=t)$',if(random3a=1 and random3b=0, '$P(B=r|S=l)/P(S=l)$',if(random3a=0 and random3b=1, '$P(B=c|S=t)/P(S=t)$',if(random3a=1 and random3b=1, '$P(B=c|S=l)/P(S=l)$',0))))", "description": "", "templateType": "anything", "can_override": false}, "condformula_advice": {"name": "condformula_advice", "group": "Conditional Probability", "definition": "if(random3a=0, '$P(S=t)$', if(random3a=1, '$P(S=l)$', 0))", "description": "", "templateType": "anything", "can_override": false}}, "variablesTest": {"condition": "", "maxRuns": 100}, "ungrouped_variables": ["rt", "ct", "rl", "cl", "random", "cttext", "rttext", "cltext", "rltext"], "variable_groups": [{"name": "probabilities set 0", "variables": ["rt0", "rttext0", "ct0", "cttext0", "rl0", "rltext0", "cl0", "cltext0"]}, {"name": "Read off table - joint probability", "variables": ["random1", "jointpdfchoice", "jointpdf", "notation", "jointpdftext"]}, {"name": "marginal probability", "variables": ["random2", "size", "sizeprob", "sizenotation", "sizesumnotation", "bee", "beeprob", "beenotation", "beesumnotation"]}, {"name": "Conditional Probability", "variables": ["random3a", "random3b", "sizecond", "beecond", "condnotation", "condformula", "condnotation2", "cond2formula", "condprob", "condnum", "conddenom", "condformula_advice"]}, {"name": "probabilities set 1", "variables": ["rt1", "ct1", "rl1", "cl1", "rttext1", "cttext1", "rltext1", "cltext1"]}], "functions": {}, "preamble": {"js": "", "css": ""}, "parts": [{"type": "numberentry", "useCustomName": true, "customName": "a)", "marks": 1, "scripts": {}, "customMarkingAlgorithm": "", "extendBaseMarkingAlgorithm": true, "unitTests": [], "showCorrectAnswer": true, "showFeedbackIcon": true, "variableReplacements": [], "variableReplacementStrategy": "originalfirst", "nextParts": [], "suggestGoingBack": false, "adaptiveMarkingPenalty": 0, "exploreObjective": null, "prompt": "

Reading off the table, what is the joint probability of the bee being {jointpdfchoice}, i.e., {notation}.

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What is the marginal probability of the bee being {size}, i.e., {sizenotation}?

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What is the marginal probability of the bee being a {bee} bumblee, i.e., {beenotation}?

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Conditional probability: given the bee is {sizecond}, what is the probability that it is a {beecond} bumblee, i.e., {condnotation}?

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What is {condnotation2}?

\n

(You could check that {condnotation} and {condnotation2} sum to one).

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Which formula could we use to show that the two random variables aren't independent?

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