Question : Find the average of odd numbers from 15 to 339
Correct Answer 177
Solution & Explanation
Solution
Method (1) to find the average of the odd numbers from 15 to 339
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 15 to 339 are
15, 17, 19, . . . . 339
After observing the above list of the odd numbers from 15 to 339 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 15 to 339 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 15 to 339
The First Term (a) = 15
The Common Difference (d) = 2
And the last term (ℓ) = 339
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 15 to 339
= 15 + 339/2
= 354/2 = 177
Thus, the average of the odd numbers from 15 to 339 = 177 Answer
Method (2) to find the average of the odd numbers from 15 to 339
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 15 to 339 are
15, 17, 19, . . . . 339
The odd numbers from 15 to 339 form an Arithmetic Series in which
The First Term (a) = 15
The Common Difference (d) = 2
And the last term (ℓ) = 339
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 15 to 339
339 = 15 + (n – 1) × 2
⇒ 339 = 15 + 2 n – 2
⇒ 339 = 15 – 2 + 2 n
⇒ 339 = 13 + 2 n
After transposing 13 to LHS
⇒ 339 – 13 = 2 n
⇒ 326 = 2 n
After rearranging the above expression
⇒ 2 n = 326
After transposing 2 to RHS
⇒ n = 326/2
⇒ n = 163
Thus, the number of terms of odd numbers from 15 to 339 = 163
This means 339 is the 163th term.
Finding the sum of the given odd numbers from 15 to 339
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 15 to 339
= 163/2 (15 + 339)
= 163/2 × 354
= 163 × 354/2
= 57702/2 = 28851
Thus, the sum of all terms of the given odd numbers from 15 to 339 = 28851
And, the total number of terms = 163
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 15 to 339
= 28851/163 = 177
Thus, the average of the given odd numbers from 15 to 339 = 177 Answer
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