Given: Of three numbers, the second number is 5 more than the average of the first and the third number. The third number is 6 more than the first number. Formula: Average of n numbers a1, a2, ..., an = (a1 + a2 + ... + an)/n Calculation: Let the three numbers be a, b and c. According to question b−(a+c)/2=5 ⇒2b–a–c=10 ----(1) And c–a=6 ⇒c=a+6 Put the value of c in equation (1) we get, 2b–a–(a+6)=10 ⇒2b–a–a–6=10 ⇒2b–2a=16 ⇒2(b–a)=16 ⇒b–a=8 ∴ difference between first and second no. is 8.