Question:
Find the average of odd numbers from 9 to 1201
Correct Answer
605
Solution And Explanation
Solution
Method (1) to find the average of the odd numbers from 9 to 1201
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 9 to 1201 are
9, 11, 13, . . . . 1201
After observing the above list of the odd numbers from 9 to 1201 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 9 to 1201 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 9 to 1201
The First Term (a) = 9
The Common Difference (d) = 2
And the last term (ℓ) = 1201
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 1201
= 9 + 1201/2
= 1210/2 = 605
Thus, the average of the odd numbers from 9 to 1201 = 605 Answer
Method (2) to find the average of the odd numbers from 9 to 1201
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 9 to 1201 are
9, 11, 13, . . . . 1201
The odd numbers from 9 to 1201 form an Arithmetic Series in which
The First Term (a) = 9
The Common Difference (d) = 2
And the last term (ℓ) = 1201
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 1201
1201 = 9 + (n – 1) × 2
⇒ 1201 = 9 + 2 n – 2
⇒ 1201 = 9 – 2 + 2 n
⇒ 1201 = 7 + 2 n
After transposing 7 to LHS
⇒ 1201 – 7 = 2 n
⇒ 1194 = 2 n
After rearranging the above expression
⇒ 2 n = 1194
After transposing 2 to RHS
⇒ n = 1194/2
⇒ n = 597
Thus, the number of terms of odd numbers from 9 to 1201 = 597
This means 1201 is the 597th term.
Finding the sum of the given odd numbers from 9 to 1201
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 1201
= 597/2 (9 + 1201)
= 597/2 × 1210
= 597 × 1210/2
= 722370/2 = 361185
Thus, the sum of all terms of the given odd numbers from 9 to 1201 = 361185
And, the total number of terms = 597
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 1201
= 361185/597 = 605
Thus, the average of the given odd numbers from 9 to 1201 = 605 Answer
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