Question : Find the average of odd numbers from 15 to 387
Correct Answer 201
Solution & Explanation
Solution
Method (1) to find the average of the odd numbers from 15 to 387
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 15 to 387 are
15, 17, 19, . . . . 387
After observing the above list of the odd numbers from 15 to 387 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 15 to 387 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 15 to 387
The First Term (a) = 15
The Common Difference (d) = 2
And the last term (ℓ) = 387
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 387
= 15 + 387/2
= 402/2 = 201
Thus, the average of the odd numbers from 15 to 387 = 201 Answer
Method (2) to find the average of the odd numbers from 15 to 387
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 15 to 387 are
15, 17, 19, . . . . 387
The odd numbers from 15 to 387 form an Arithmetic Series in which
The First Term (a) = 15
The Common Difference (d) = 2
And the last term (ℓ) = 387
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 387
387 = 15 + (n – 1) × 2
⇒ 387 = 15 + 2 n – 2
⇒ 387 = 15 – 2 + 2 n
⇒ 387 = 13 + 2 n
After transposing 13 to LHS
⇒ 387 – 13 = 2 n
⇒ 374 = 2 n
After rearranging the above expression
⇒ 2 n = 374
After transposing 2 to RHS
⇒ n = 374/2
⇒ n = 187
Thus, the number of terms of odd numbers from 15 to 387 = 187
This means 387 is the 187th term.
Finding the sum of the given odd numbers from 15 to 387
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 387
= 187/2 (15 + 387)
= 187/2 × 402
= 187 × 402/2
= 75174/2 = 37587
Thus, the sum of all terms of the given odd numbers from 15 to 387 = 37587
And, the total number of terms = 187
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 387
= 37587/187 = 201
Thus, the average of the given odd numbers from 15 to 387 = 201 Answer
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