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**emily9843** I can find out the mean, but not S.D /variance. How can I do this? Please show your steps so that I can understand. Thank you

A class of 20 students takes a test. The score, x, for each student was recorded by the teacher. The results are summarized by

Σ(x-10) = 208 and Σ(x-10)² = 2716

(i) Calculate the standard deviation of the 20 scores.

(ii) Show that Σx² = 8876.

(iii) Two other students took the test later. Their scores were 18 and 16. Find the mean and standard deviation of all 22 scores.