Question : Find the average of odd numbers from 11 to 769
Correct Answer 390
Solution & Explanation
Solution
Method (1) to find the average of the odd numbers from 11 to 769
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 11 to 769 are
11, 13, 15, . . . . 769
After observing the above list of the odd numbers from 11 to 769 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 11 to 769 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 11 to 769
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 769
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 769
= 11 + 769/2
= 780/2 = 390
Thus, the average of the odd numbers from 11 to 769 = 390 Answer
Method (2) to find the average of the odd numbers from 11 to 769
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 11 to 769 are
11, 13, 15, . . . . 769
The odd numbers from 11 to 769 form an Arithmetic Series in which
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 769
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 769
769 = 11 + (n – 1) × 2
⇒ 769 = 11 + 2 n – 2
⇒ 769 = 11 – 2 + 2 n
⇒ 769 = 9 + 2 n
After transposing 9 to LHS
⇒ 769 – 9 = 2 n
⇒ 760 = 2 n
After rearranging the above expression
⇒ 2 n = 760
After transposing 2 to RHS
⇒ n = 760/2
⇒ n = 380
Thus, the number of terms of odd numbers from 11 to 769 = 380
This means 769 is the 380th term.
Finding the sum of the given odd numbers from 11 to 769
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 769
= 380/2 (11 + 769)
= 380/2 × 780
= 380 × 780/2
= 296400/2 = 148200
Thus, the sum of all terms of the given odd numbers from 11 to 769 = 148200
And, the total number of terms = 380
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 769
= 148200/380 = 390
Thus, the average of the given odd numbers from 11 to 769 = 390 Answer
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