Answer:
New Average of New List = 87.5
Step-by-step explanation:
Average is the arithmetic mean (M) of observations.
M = ΣX / N
where ΣX = sum of all observations , N = number of observations
Given : M = 90 ; N = 40
M = ΣX / N
90 = ΣX / 4
ΣX = 90 x 4
ΣX = 360 [ Of Old List of 4 numbers ]
New ΣX of new list of 4th new number = Old ΣX - Old 4th No. + New 4th No.
New ΣX = 360 - 90 + 80
New ΣX = 350
New Average (Mean M) = New ΣX / N
New M = 350 / 4
New M = 87.5
