Question:
Find the average of odd numbers from 9 to 1339
Correct Answer
674
Solution And Explanation
Solution
Method (1) to find the average of the odd numbers from 9 to 1339
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 9 to 1339 are
9, 11, 13, . . . . 1339
After observing the above list of the odd numbers from 9 to 1339 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 9 to 1339 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 9 to 1339
The First Term (a) = 9
The Common Difference (d) = 2
And the last term (ℓ) = 1339
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 9 to 1339
= 9 + 1339/2
= 1348/2 = 674
Thus, the average of the odd numbers from 9 to 1339 = 674 Answer
Method (2) to find the average of the odd numbers from 9 to 1339
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 9 to 1339 are
9, 11, 13, . . . . 1339
The odd numbers from 9 to 1339 form an Arithmetic Series in which
The First Term (a) = 9
The Common Difference (d) = 2
And the last term (ℓ) = 1339
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 9 to 1339
1339 = 9 + (n – 1) × 2
⇒ 1339 = 9 + 2 n – 2
⇒ 1339 = 9 – 2 + 2 n
⇒ 1339 = 7 + 2 n
After transposing 7 to LHS
⇒ 1339 – 7 = 2 n
⇒ 1332 = 2 n
After rearranging the above expression
⇒ 2 n = 1332
After transposing 2 to RHS
⇒ n = 1332/2
⇒ n = 666
Thus, the number of terms of odd numbers from 9 to 1339 = 666
This means 1339 is the 666th term.
Finding the sum of the given odd numbers from 9 to 1339
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 9 to 1339
= 666/2 (9 + 1339)
= 666/2 × 1348
= 666 × 1348/2
= 897768/2 = 448884
Thus, the sum of all terms of the given odd numbers from 9 to 1339 = 448884
And, the total number of terms = 666
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 9 to 1339
= 448884/666 = 674
Thus, the average of the given odd numbers from 9 to 1339 = 674 Answer
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