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Course: Statistics — Third Secondary
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Discrete Random Variables

Statistics — Third Secondary

Discrete Random Variables

Common mistakes

Common mistakes

Comparison aspectMain ideaKeywords
Forgetting that the probabilities add up to 1
  • if this condition fails
  • the table is wrong
conditionfailstablewrong
Confusing P(X < 3) with P(X ≤ 3)the value 3 is included in the second but not in the firstvalueincludedsecondfirst
Including a value outside the rangethe probability of any value outside the range of the variable is zeroprobabilityvariablezero
Treating a probability as a value of the variable
  • f(x) is a probability
  • while x is the value the variable takes
whiletakes
Not listing all the outcomes
  • when a die is rolled twice
  • all 36 ordered pairs must be counted
rolledtwiceorderedpairs
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