Question : Find the average of odd numbers from 9 to 1481
Correct Answer 745
Solution & Explanation
Solution
Method (1) to find the average of the odd numbers from 9 to 1481
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 9 to 1481 are
9, 11, 13, . . . . 1481
After observing the above list of the odd numbers from 9 to 1481 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 9 to 1481 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 9 to 1481
The First Term (a) = 9
The Common Difference (d) = 2
And the last term (ℓ) = 1481
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 1481
= 9 + 1481/2
= 1490/2 = 745
Thus, the average of the odd numbers from 9 to 1481 = 745 Answer
Method (2) to find the average of the odd numbers from 9 to 1481
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 9 to 1481 are
9, 11, 13, . . . . 1481
The odd numbers from 9 to 1481 form an Arithmetic Series in which
The First Term (a) = 9
The Common Difference (d) = 2
And the last term (ℓ) = 1481
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 1481
1481 = 9 + (n – 1) × 2
⇒ 1481 = 9 + 2 n – 2
⇒ 1481 = 9 – 2 + 2 n
⇒ 1481 = 7 + 2 n
After transposing 7 to LHS
⇒ 1481 – 7 = 2 n
⇒ 1474 = 2 n
After rearranging the above expression
⇒ 2 n = 1474
After transposing 2 to RHS
⇒ n = 1474/2
⇒ n = 737
Thus, the number of terms of odd numbers from 9 to 1481 = 737
This means 1481 is the 737th term.
Finding the sum of the given odd numbers from 9 to 1481
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 1481
= 737/2 (9 + 1481)
= 737/2 × 1490
= 737 × 1490/2
= 1098130/2 = 549065
Thus, the sum of all terms of the given odd numbers from 9 to 1481 = 549065
And, the total number of terms = 737
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 1481
= 549065/737 = 745
Thus, the average of the given odd numbers from 9 to 1481 = 745 Answer
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