Question:
Find the average of odd numbers from 15 to 623
Correct Answer
319
Solution And Explanation
Solution
Method (1) to find the average of the odd numbers from 15 to 623
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 15 to 623 are
15, 17, 19, . . . . 623
After observing the above list of the odd numbers from 15 to 623 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 15 to 623 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 15 to 623
The First Term (a) = 15
The Common Difference (d) = 2
And the last term (ℓ) = 623
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 623
= 15 + 623/2
= 638/2 = 319
Thus, the average of the odd numbers from 15 to 623 = 319 Answer
Method (2) to find the average of the odd numbers from 15 to 623
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 15 to 623 are
15, 17, 19, . . . . 623
The odd numbers from 15 to 623 form an Arithmetic Series in which
The First Term (a) = 15
The Common Difference (d) = 2
And the last term (ℓ) = 623
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 623
623 = 15 + (n – 1) × 2
⇒ 623 = 15 + 2 n – 2
⇒ 623 = 15 – 2 + 2 n
⇒ 623 = 13 + 2 n
After transposing 13 to LHS
⇒ 623 – 13 = 2 n
⇒ 610 = 2 n
After rearranging the above expression
⇒ 2 n = 610
After transposing 2 to RHS
⇒ n = 610/2
⇒ n = 305
Thus, the number of terms of odd numbers from 15 to 623 = 305
This means 623 is the 305th term.
Finding the sum of the given odd numbers from 15 to 623
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 623
= 305/2 (15 + 623)
= 305/2 × 638
= 305 × 638/2
= 194590/2 = 97295
Thus, the sum of all terms of the given odd numbers from 15 to 623 = 97295
And, the total number of terms = 305
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 623
= 97295/305 = 319
Thus, the average of the given odd numbers from 15 to 623 = 319 Answer
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