Question:
Find the average of odd numbers from 9 to 1489
Correct Answer
749
Solution And Explanation
Solution
Method (1) to find the average of the odd numbers from 9 to 1489
Shortcut Trick to find the average of the given continuous odd numbers
The odd numbers from 9 to 1489 are
9, 11, 13, . . . . 1489
After observing the above list of the odd numbers from 9 to 1489 we find that the difference between two consecutive terms are equal. This means the list of the odd numbers from 9 to 1489 form an Arithmetic Series.
In the Arithmetic Series of the odd numbers from 9 to 1489
The First Term (a) = 9
The Common Difference (d) = 2
And the last term (ℓ) = 1489
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 1489
= 9 + 1489/2
= 1498/2 = 749
Thus, the average of the odd numbers from 9 to 1489 = 749 Answer
Method (2) to find the average of the odd numbers from 9 to 1489
Finding the average of given continuous odd numbers after finding their sum
The odd numbers from 9 to 1489 are
9, 11, 13, . . . . 1489
The odd numbers from 9 to 1489 form an Arithmetic Series in which
The First Term (a) = 9
The Common Difference (d) = 2
And the last term (ℓ) = 1489
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 1489
1489 = 9 + (n – 1) × 2
⇒ 1489 = 9 + 2 n – 2
⇒ 1489 = 9 – 2 + 2 n
⇒ 1489 = 7 + 2 n
After transposing 7 to LHS
⇒ 1489 – 7 = 2 n
⇒ 1482 = 2 n
After rearranging the above expression
⇒ 2 n = 1482
After transposing 2 to RHS
⇒ n = 1482/2
⇒ n = 741
Thus, the number of terms of odd numbers from 9 to 1489 = 741
This means 1489 is the 741th term.
Finding the sum of the given odd numbers from 9 to 1489
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 1489
= 741/2 (9 + 1489)
= 741/2 × 1498
= 741 × 1498/2
= 1110018/2 = 555009
Thus, the sum of all terms of the given odd numbers from 9 to 1489 = 555009
And, the total number of terms = 741
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 1489
= 555009/741 = 749
Thus, the average of the given odd numbers from 9 to 1489 = 749 Answer
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