Question:
Find the average of even numbers from 10 to 800
Correct Answer
405
Solution And Explanation
Solution
Method (1) to find the average of the even numbers from 10 to 800
Shortcut Trick to find the average of the given continuous even numbers
The even numbers from 10 to 800 are
10, 12, 14, . . . . 800
After observing the above list of the even numbers from 10 to 800 we find that the difference between two consecutive terms are equal. This means the list of the even numbers from 10 to 800 form an Arithmetic Series.
In the Arithmetic Series of the even numbers from 10 to 800
The First Term (a) = 10
The Common Difference (d) = 2
And the last term (ℓ) = 800
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 800
= 10 + 800/2
= 810/2 = 405
Thus, the average of the even numbers from 10 to 800 = 405 Answer
Method (2) to find the average of the even numbers from 10 to 800
Finding the average of given continuous even numbers after finding their sum
The even numbers from 10 to 800 are
10, 12, 14, . . . . 800
The even numbers from 10 to 800 form an Arithmetic Series in which
The First Term (a) = 10
The Common Difference (d) = 2
And the last term (ℓ) = 800
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 800
800 = 10 + (n – 1) × 2
⇒ 800 = 10 + 2 n – 2
⇒ 800 = 10 – 2 + 2 n
⇒ 800 = 8 + 2 n
After transposing 8 to LHS
⇒ 800 – 8 = 2 n
⇒ 792 = 2 n
After rearranging the above expression
⇒ 2 n = 792
After transposing 2 to RHS
⇒ n = 792/2
⇒ n = 396
Thus, the number of terms of even numbers from 10 to 800 = 396
This means 800 is the 396th term.
Finding the sum of the given even numbers from 10 to 800
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 800
= 396/2 (10 + 800)
= 396/2 × 810
= 396 × 810/2
= 320760/2 = 160380
Thus, the sum of all terms of the given even numbers from 10 to 800 = 160380
And, the total number of terms = 396
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 800
= 160380/396 = 405
Thus, the average of the given even numbers from 10 to 800 = 405 Answer
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