The average of 10 observations is 21. A new observation is included and the average of these 11 numbers is 1 less than the prevoius average. The observation is ______.
Explanation:
Original average = 21, new average = 21 - 1 = 20
Sum of the 10 observations = 10 × 21 = 210
Let the number added be 'x'.
New sum = 210 + x = 11 × 20
⇒ x = 220 - 210 = 10
Hence, option (b).