Shortcut Trick
For an Arithmetic Progression (AP), Average = (First term + Last term) ÷ 2.
First multiple of 8 = 8 × 1 = 8.
Fourth multiple of 8 = 8 × 4 = 32.
Average = (8 + 32) ÷ 2 = 40 ÷ 2 = 20.
∴ The correct answer is 20.
Alternate Method
Given: First four positive multiples of 8.
Formula Used: Average = Sum of observations ÷ Number of observations
⇒ First four multiples are: 8, 16, 24, 32
⇒ Sum = 8 + 16 + 24 + 32
⇒ Sum = 80
⇒ Average = 80 ÷ 4
⇒ Average = 20
∴ The correct answer is 20.
Additional Information
Average of Multiples
The average of the first 'n' multiples of a number 'k' is given by the formula: k × (n + 1) ÷ 2.
Arithmetic Progression (AP)
Multiples of any number always form an AP with a common difference equal to the number itself.
Sum of n terms in AP
Sum = (n ÷ 2) × [2a + (n − 1)d], where 'a' is the first term and 'd' is the common difference.