What is the average of 72, 74, 76, 78, 80, 82, 84, 86 ?

All are consecutive even numbers starting from 72 to 86. Total numbers are 8. If total numbers are even then average is average of middle two numbers..

as n is even, avg =$\frac{\mathbf{78}\mathbf{+}\mathbf{80}}{\mathbf{2}}\mathbf{=}\frac{\mathbf{158}}{\mathbf{2}}\mathbf{=}\mathbf{79}$