The average of 30 numbers is 12. The average of the first 20 of them is 11 and that of the next 9 is 10. The last number is
Options:
A . 45
B . 50
C . 40
D . 60
Answer: Option B Answer: (b)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 Last number = 30 × 12 – 20 × 11 – 9 × 10 = 360 – 220 – 90 = 360 – 310 = 50
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