Given: 8 multiples of 13 Formula Used: Arithmetic mean = Sum of terms/Number of terms Sum of an arithmetic progression = (number of terms/2) × ( first term + last term) nth term of an Arithmetic progression = first term + (n – 1) × common difference Common difference = second term – first term Calculation: multiple of 13 ⇒ common difference = 13 First term = 13 8th term =13+(8–1)13 ⇒ 8th term =13+91
⇒ 8th term =104 Sum of arithmetic progression =(8/2)×(13+104) ⇒4×117 ⇒468 Arithmetic mean =468/8 ⇒58.5 ∴ Arithmetic mean of first 8 multiples of 13 is 58.5