Property 3. (Mean of the composite series ). If X; i = 1, 2,..., k ) are the means of kcomponent series of sizes ni , ( i = 1, 2,..., k ) respectively, then the mean x of the compositeseries obtained on combining the component series is given by the formula :%3Dkk1, X1 + N2 X2 + .. + ng Ixn1 + N2 + ... + Nk+ Nx XkN¡ X; /%3DNj%3Di=1i=118

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Property 3. (Mean of the composite series ). If xi (i = 1, 2,..., k ) are the means of k component series of sizes n¡ , ( i =1, 2,...., k ) respectively, then the mean x of the composik series obtained on combining the component series is given by the formula : k 111 x1 +12 X2+ n, + N2 + ... + nk ... N¡ X¡ i=1 Ni i=1 %3D