Given observations : 7, 10, 13, 16, ......., 121The above observation are in A.P and σ is their S.D. 7,10,13,16,......121(×7+1)↓↓↓↓↓50,71,92,113......848The second set of observations is obtained by multiplying observations of the first set by 7 and adding 1 to the product.∴Required S.D of (50, 71, 92, 113, ........, 848) = 7σ