Question : Find the average of even numbers from 10 to 660
Correct Answer 335
Solution & Explanation
Solution
Method (1) to find the average of the even numbers from 10 to 660
Shortcut Trick to find the average of the given continuous even numbers
The even numbers from 10 to 660 are
10, 12, 14, . . . . 660
After observing the above list of the even numbers from 10 to 660 we find that the difference between two consecutive terms are equal. This means the list of the even numbers from 10 to 660 form an Arithmetic Series.
In the Arithmetic Series of the even numbers from 10 to 660
The First Term (a) = 10
The Common Difference (d) = 2
And the last term (ℓ) = 660
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 even numbers from 10 to 660
= 10 + 660/2
= 670/2 = 335
Thus, the average of the even numbers from 10 to 660 = 335 Answer
Method (2) to find the average of the even numbers from 10 to 660
Finding the average of given continuous even numbers after finding their sum
The even numbers from 10 to 660 are
10, 12, 14, . . . . 660
The even numbers from 10 to 660 form an Arithmetic Series in which
The First Term (a) = 10
The Common Difference (d) = 2
And the last term (ℓ) = 660
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 even numbers from 10 to 660
660 = 10 + (n – 1) × 2
⇒ 660 = 10 + 2 n – 2
⇒ 660 = 10 – 2 + 2 n
⇒ 660 = 8 + 2 n
After transposing 8 to LHS
⇒ 660 – 8 = 2 n
⇒ 652 = 2 n
After rearranging the above expression
⇒ 2 n = 652
After transposing 2 to RHS
⇒ n = 652/2
⇒ n = 326
Thus, the number of terms of even numbers from 10 to 660 = 326
This means 660 is the 326th term.
Finding the sum of the given even numbers from 10 to 660
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 even numbers from 10 to 660
= 326/2 (10 + 660)
= 326/2 × 670
= 326 × 670/2
= 218420/2 = 109210
Thus, the sum of all terms of the given even numbers from 10 to 660 = 109210
And, the total number of terms = 326
Since, the average of the given numbers
= Sum of the given numbers/Total number of given numbers
Thus, the average of the given even numbers from 10 to 660
= 109210/326 = 335
Thus, the average of the given even numbers from 10 to 660 = 335 Answer
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