Question:
Find the average of even numbers from 10 to 128
Correct Answer
69
Solution And Explanation
Solution
Method (1) to find the average of the even numbers from 10 to 128
Shortcut Trick to find the average of the given continuous even numbers
The even numbers from 10 to 128 are
10, 12, 14, . . . . 128
After observing the above list of the even numbers from 10 to 128 we find that the difference between two consecutive terms are equal. This means the list of the even numbers from 10 to 128 form an Arithmetic Series.
In the Arithmetic Series of the even numbers from 10 to 128
The First Term (a) = 10
The Common Difference (d) = 2
And the last term (ℓ) = 128
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 128
= 10 + 128/2
= 138/2 = 69
Thus, the average of the even numbers from 10 to 128 = 69 Answer
Method (2) to find the average of the even numbers from 10 to 128
Finding the average of given continuous even numbers after finding their sum
The even numbers from 10 to 128 are
10, 12, 14, . . . . 128
The even numbers from 10 to 128 form an Arithmetic Series in which
The First Term (a) = 10
The Common Difference (d) = 2
And the last term (ℓ) = 128
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 128
128 = 10 + (n – 1) × 2
⇒ 128 = 10 + 2 n – 2
⇒ 128 = 10 – 2 + 2 n
⇒ 128 = 8 + 2 n
After transposing 8 to LHS
⇒ 128 – 8 = 2 n
⇒ 120 = 2 n
After rearranging the above expression
⇒ 2 n = 120
After transposing 2 to RHS
⇒ n = 120/2
⇒ n = 60
Thus, the number of terms of even numbers from 10 to 128 = 60
This means 128 is the 60th term.
Finding the sum of the given even numbers from 10 to 128
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 128
= 60/2 (10 + 128)
= 60/2 × 138
= 60 × 138/2
= 8280/2 = 4140
Thus, the sum of all terms of the given even numbers from 10 to 128 = 4140
And, the total number of terms = 60
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 128
= 4140/60 = 69
Thus, the average of the given even numbers from 10 to 128 = 69 Answer
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