Given:
The average of a, b, c and d = 30
The average of a, b, c and e = 40
Formula used: Average = (Sum of observations)/(Number of observations)
Calculations:
Average of a, b, c and d = 30
⇒(a+b+c+d)/4=30 ⇒(a+b+c+d)=120 ----(i)
Average of a, b, c and e = 40
⇒(a+b+c+e)/4=40 ⇒(a+b+c+e)=160 ----(ii)
Subtracting equation (i) from (ii),
(a+b+c+e)−(a+b+c+d)=160−120
⇒e−d=40 ∴ The difference between e and d is 40.