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प्रश्न
If the p.m.f. of a d.r.v. X is P(X = x) = `{{:(x/("n"("n" + 1))",", "for" x = 1"," 2"," 3"," .... "," "n"),(0",", "otherwise"):}`, then E(X) = ______
विकल्प
`"n" + 1/2`
`"n"/3 + 1/6`
`"n"/2 + 1/5`
`"n" + 1/3`
उत्तर
`"n"/3 + 1/6`
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