Question : Find the average of odd numbers from 11 to 607
Correct Answer 309
Solution & Explanation
Solution
Method (1) to find the average of the odd numbers from 11 to 607
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 11 to 607 are
11, 13, 15, . . . . 607
After observing the above list of the odd numbers from 11 to 607 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 11 to 607 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 11 to 607
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 607
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 607
= 11 + 607/2
= 618/2 = 309
Thus, the average of the odd numbers from 11 to 607 = 309 Answer
Method (2) to find the average of the odd numbers from 11 to 607
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 11 to 607 are
11, 13, 15, . . . . 607
The odd numbers from 11 to 607 form an Arithmetic Series in which
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 607
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 607
607 = 11 + (n – 1) × 2
⇒ 607 = 11 + 2 n – 2
⇒ 607 = 11 – 2 + 2 n
⇒ 607 = 9 + 2 n
After transposing 9 to LHS
⇒ 607 – 9 = 2 n
⇒ 598 = 2 n
After rearranging the above expression
⇒ 2 n = 598
After transposing 2 to RHS
⇒ n = 598/2
⇒ n = 299
Thus, the number of terms of odd numbers from 11 to 607 = 299
This means 607 is the 299th term.
Finding the sum of the given odd numbers from 11 to 607
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 607
= 299/2 (11 + 607)
= 299/2 × 618
= 299 × 618/2
= 184782/2 = 92391
Thus, the sum of all terms of the given odd numbers from 11 to 607 = 92391
And, the total number of terms = 299
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 607
= 92391/299 = 309
Thus, the average of the given odd numbers from 11 to 607 = 309 Answer
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