Out of four numbers, the average of the first three is 18 and that of the last three is 16. If the last number is 19, the first is
Options:
A .  18
B .  25
C .  20
D .  19
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 × na + b + c = 18 × 3 = 54 and, b + c + d = 16 × 3 = 48 ∴ a + b + c – b – c – d ⇒ 54 – 48 = 6 ⇒ a – d = 6 ⇒ a – 19 = 6 ⇒ a = 19 + 6 = 25
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