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Ex 13.4, 16 - Mean numbers obtained on throwing a die - Mean or Expectation of random variable

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  1. Chapter 13 Class 12 Probability
  2. Serial order wise
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Ex 13.4, 16 The mean of the numbers obtained on throwing a die having written 1 on three faces, 2 on two faces and 5 on one face is (A) 1 (B) 2 (C) 5 (D) 8﷮3﷯ Let, X be the number obtained on throwing the die Since on throwing a die, we can get 1, 2 or 5 Value of X can be 1, 2 or 5 So, The Probability are given by P(X = 1) = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑓𝑎𝑐𝑒𝑠 1 𝑖𝑠 𝑤𝑟𝑖𝑡𝑡𝑒𝑛 ﷮𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑎𝑐𝑒𝑠﷯ = 3﷮6﷯ = 1﷮2﷯ P(X = 2) = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑓𝑎𝑐𝑒𝑠 2 𝑖𝑠 𝑤𝑟𝑖𝑡𝑡𝑒𝑛 ﷮𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑎𝑐𝑒𝑠﷯ = 2﷮6﷯ = 1﷮3﷯ P(x = 5) = 𝑁𝑢𝑚𝑏𝑒𝑟 𝑓𝑎𝑐𝑒𝑠 5 𝑖𝑠 𝑤𝑟𝑖𝑡𝑡𝑒𝑛 ﷮𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑓𝑎𝑐𝑒𝑠﷯ = 1﷮6﷯ Hence the Probability distribution : The Mean of the number is given by 𝝁=𝑬 𝑿﷯= 𝑖 = 1﷮𝑛﷮𝑥𝑖𝑝𝑖﷯ = 1 × 1﷮2﷯+2 × 1﷮3﷯+ 5 × 1﷮6﷯ = 1﷮2﷯+ 2﷮3﷯+ 5﷮6﷯ = 3 + 4 + 5﷮6﷯ = 12﷮6﷯ = 2 Hence option B is correct

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Davneet Singh
Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He provides courses for Mathematics from Class 9 to 12. You can ask questions here.
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