The mean of a set of 30 observation is 75 . If each observations is multiplied by non-zero number λ and then each of them is decreased by 25 , their mean remains the same. Then, λ is equal to :

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Let 30 observations be x 1 , x 2 , . . . . . … , x 30 . Given mean = 75 ⇒ x 1 + x 2 + … + x 30 = 75 × 30 Now according to question, λ ( x 1 + x 2 + … + x 30 ) - 25 × 30 30 = 75 × 30 30 ⇒ λ 75 × 30 = 100 × 30 ⇒ λ = 4 3

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