Question : Find the average of odd numbers from 11 to 371
Correct Answer 191
Solution & Explanation
Solution
Method (1) to find the average of the odd numbers from 11 to 371
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 11 to 371 are
11, 13, 15, . . . . 371
After observing the above list of the odd numbers from 11 to 371 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 11 to 371 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 11 to 371
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 371
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 371
= 11 + 371/2
= 382/2 = 191
Thus, the average of the odd numbers from 11 to 371 = 191 Answer
Method (2) to find the average of the odd numbers from 11 to 371
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 11 to 371 are
11, 13, 15, . . . . 371
The odd numbers from 11 to 371 form an Arithmetic Series in which
The First Term (a) = 11
The Common Difference (d) = 2
And the last term (ℓ) = 371
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 371
371 = 11 + (n – 1) × 2
⇒ 371 = 11 + 2 n – 2
⇒ 371 = 11 – 2 + 2 n
⇒ 371 = 9 + 2 n
After transposing 9 to LHS
⇒ 371 – 9 = 2 n
⇒ 362 = 2 n
After rearranging the above expression
⇒ 2 n = 362
After transposing 2 to RHS
⇒ n = 362/2
⇒ n = 181
Thus, the number of terms of odd numbers from 11 to 371 = 181
This means 371 is the 181th term.
Finding the sum of the given odd numbers from 11 to 371
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 371
= 181/2 (11 + 371)
= 181/2 × 382
= 181 × 382/2
= 69142/2 = 34571
Thus, the sum of all terms of the given odd numbers from 11 to 371 = 34571
And, the total number of terms = 181
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 371
= 34571/181 = 191
Thus, the average of the given odd numbers from 11 to 371 = 191 Answer
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