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Find the positive value of x if the standard deviation of...

Find the positive value of x if the standard deviation of the numbers 1, x + 1, 2x + 1 is 6

A.

1

B.

2

C.

3

D.

4

Correct answer is C

mean (x) = 1+x+1+2x+13

= 3x+33

= 1 + x

X(XX)(XX)21xx2x+1002x+1xx22x2

S.D = (x7)2f

= (6)2

= 2x23

= 2x2

= 18

x2 = 9

∴ x = ± 9

= ±3