The average of 20 numbers is 12. The average of the first 12 numbers is 11 and that of the next 7 numbers is 10. The last number is :
Options:
A . 38
B . 50
C . 48
D . 40
Answer: Option A Answer: (a) Using Rule 1, Average of two or more numbers/quantities is called the mean of these numbers, which is given by $\text"Average(A)" = \text"Sum of observation / quantities"/\text"No of observation / quantities"$ ∴ S = A × n Last number = Sum of 20 numbers – sum of first 12 numbers – sum of next 7 numbers = 20 × 12 – 11 × 12 – 7 × 10 = 240 – 132 – 70 = 38
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