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General
Easy

Question

If X is a random variable with the following distribution

where p + q = 1 then the variance of X is

  1. a p plus b q    
  2. a p minus b q    
  3. p q left parenthesis a minus b right parenthesis to the power of 2 end exponent    
  4. p q left parenthesis a plus b right parenthesis to the power of 2 end exponent    

The correct answer is: p q left parenthesis a minus b right parenthesis to the power of 2 end exponent


    table row cell text end text text M end text text e end text text a end text text n end text text end text text o end text text f end text text end text X equals mu equals sum x subscript i end subscript P open parentheses X equals x subscript i end subscript close parentheses equals a p plus b q end cell row cell text end text text v end text text a end text text r end text text i end text text a end text text n end text text c end text text e end text text end text text o end text text f end text text end text X equals sigma to the power of 2 end exponent equals sum x subscript i end subscript superscript 2 end superscript P open parentheses X equals x subscript i end subscript close parentheses minus mu to the power of 2 end exponent end cell row cell equals a to the power of 2 end exponent p plus b to the power of 2 end exponent q minus left parenthesis a p plus b q right parenthesis to the power of 2 end exponent end cell row cell equals a to the power of 2 end exponent p plus b to the power of 2 end exponent q minus a to the power of 2 end exponent p to the power of 2 end exponent minus b to the power of 2 end exponent q to the power of 2 end exponent minus 2 a b p q end cell row cell equals a to the power of 2 end exponent p left parenthesis 1 minus p right parenthesis plus b to the power of 2 end exponent q left parenthesis 1 minus q right parenthesis minus 2 a b p q end cell row cell equals a to the power of 2 end exponent p q plus b to the power of 2 end exponent q p minus 2 a b p q equals p q open parentheses a to the power of 2 end exponent plus b to the power of 2 end exponent minus 2 a b close parentheses end cell row cell equals p q left parenthesis a minus b right parenthesis to the power of 2 end exponent end cell end table

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