A student was asked to find the arithmetic mean of the following 12 numbers : 3, 11, 7, 9, 15, 13, 8, 19, 17, 21, 14 and x He found the mean to be 12. The value of x will be :
Options:
A . 17
B . 31
C . 7
D . 3
Answer: Option C Answer: (c)Using Rule 1, Average of two or more numbers/quantities is called the mean of these numbers, which is given by$\text"Average(A)" = \text"Sumof observation / quantities"/\text"No of observation / quantities"$∴ S = A × n Mean = ${3 +11+ 9+7+15+ 13+ 8 +19 +17 +21 +14+x}/12$ According to question, ${137+x}/12$ = 12 ∴ 137 + x = 144 ∴ x = 144 – 137 = 7
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