The average of 10 observations is 21. A new observation is included and the average of these 11 numbers is 1 less than the previous average. The 11th observation is ______.
Answer & explanation
Correct answer: option 3
Sum of 10 numbers = 10 × 21 = 210
After adding 1 new number , Sum of 11 numbers = 11 × 20 = 220
New Added number = 220 - 210 = 10