OCR S1 2010 January — Question 4

Exam BoardOCR
ModuleS1 (Statistics 1)
Year2010
SessionJanuary
TopicDiscrete Probability Distributions
TypeCalculate Var(X) from table

4 A certain four-sided die is biased. The score, \(X\), on each throw is a random variable with probability distribution as shown in the table. Throws of the die are independent.
\(x\)0123
\(\mathrm { P } ( X = x )\)\(\frac { 1 } { 2 }\)\(\frac { 1 } { 4 }\)\(\frac { 1 } { 8 }\)\(\frac { 1 } { 8 }\)
  1. Calculate \(\mathrm { E } ( X )\) and \(\operatorname { Var } ( X )\). The die is thrown 10 times.
  2. Find the probability that there are not more than 4 throws on which the score is 1 .
  3. Find the probability that there are exactly 4 throws on which the score is 2 .