Question:
Find the average of odd numbers from 11 to 1251
Correct Answer
631
Solution And Explanation
Solution
Method (1) to find the average of the odd numbers from 11 to 1251
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 11 to 1251 are
11, 13, 15, . . . . 1251
After observing the above list of the odd numbers from 11 to 1251 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 11 to 1251 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 11 to 1251
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 1251
The average of the numbers forming an Arithmetic Series
= The first term (a) + The last term (ℓ)/2
⇒ The average of numbers forming an Arithmetic Series = a + ℓ/2
Thus, the average of the odd numbers from 11 to 1251
= 11 + 1251/2
= 1262/2 = 631
Thus, the average of the odd numbers from 11 to 1251 = 631 Answer
Method (2) to find the average of the odd numbers from 11 to 1251
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 11 to 1251 are
11, 13, 15, . . . . 1251
The odd numbers from 11 to 1251 form an Arithmetic Series in which
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 1251
The Average of the given numbers
= Sum of the given numbers/Total number of given numbers
Thus, to find the average of the given numbers, first, we need to find their sum and the total number of given numbers
Finding the number of terms
For an Arithmetic Series, the nth term
an = a + (n – 1) d
Where
a = First term
d = Common difference
n = number of terms
an = nth term
Thus, for the given series of the odd numbers from 11 to 1251
1251 = 11 + (n – 1) × 2
⇒ 1251 = 11 + 2 n – 2
⇒ 1251 = 11 – 2 + 2 n
⇒ 1251 = 9 + 2 n
After transposing 9 to LHS
⇒ 1251 – 9 = 2 n
⇒ 1242 = 2 n
After rearranging the above expression
⇒ 2 n = 1242
After transposing 2 to RHS
⇒ n = 1242/2
⇒ n = 621
Thus, the number of terms of odd numbers from 11 to 1251 = 621
This means 1251 is the 621th term.
Finding the sum of the given odd numbers from 11 to 1251
The sum of all terms (S) in an Arithmetic Series
= n/2 (a + ℓ)
Where, n = number of terms
a = First term
And, ℓ = Last term
Thus, the sum of all terms (S) of the given odd numbers from 11 to 1251
= 621/2 (11 + 1251)
= 621/2 × 1262
= 621 × 1262/2
= 783702/2 = 391851
Thus, the sum of all terms of the given odd numbers from 11 to 1251 = 391851
And, the total number of terms = 621
Since, the average of the given numbers
= Sum of the given numbers/Total number of given numbers
Thus, the average of the given odd numbers from 11 to 1251
= 391851/621 = 631
Thus, the average of the given odd numbers from 11 to 1251 = 631 Answer
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