Given: The average of certain first natural numbers is 10.5 Formula used: Average = Sum of observations/ number of observations Average of ‘first’ “n” natural numbers =
[n+1]
2
Calculation: Average of certain first natural numbers =10.5=
[n+1]
2
⇒ n + 1 = 21 ⇒ n = 20 Now, Sum of these first 20 natural numbers = average × 20 ⇒ 10.5 × 20 = 210 ∴ The sum of these numbers is 210.