Question : Find the average of odd numbers from 11 to 851
Correct Answer 431
Solution & Explanation
Solution
Method (1) to find the average of the odd numbers from 11 to 851
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 11 to 851 are
11, 13, 15, . . . . 851
After observing the above list of the odd numbers from 11 to 851 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 11 to 851 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 11 to 851
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 851
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 851
= 11 + 851/2
= 862/2 = 431
Thus, the average of the odd numbers from 11 to 851 = 431 Answer
Method (2) to find the average of the odd numbers from 11 to 851
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 11 to 851 are
11, 13, 15, . . . . 851
The odd numbers from 11 to 851 form an Arithmetic Series in which
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 851
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 851
851 = 11 + (n – 1) × 2
⇒ 851 = 11 + 2 n – 2
⇒ 851 = 11 – 2 + 2 n
⇒ 851 = 9 + 2 n
After transposing 9 to LHS
⇒ 851 – 9 = 2 n
⇒ 842 = 2 n
After rearranging the above expression
⇒ 2 n = 842
After transposing 2 to RHS
⇒ n = 842/2
⇒ n = 421
Thus, the number of terms of odd numbers from 11 to 851 = 421
This means 851 is the 421th term.
Finding the sum of the given odd numbers from 11 to 851
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 851
= 421/2 (11 + 851)
= 421/2 × 862
= 421 × 862/2
= 362902/2 = 181451
Thus, the sum of all terms of the given odd numbers from 11 to 851 = 181451
And, the total number of terms = 421
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 851
= 181451/421 = 431
Thus, the average of the given odd numbers from 11 to 851 = 431 Answer
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