Average means the central or middle value of a group of numbers. If your scores in 3 tests are 70, 80 and 90 — your average score is (70+80+90)/3 = 80. Simple! Average = Sum of all values / Number of values.
Key Formulas
Basic Average
Average = Sum of observations / Number of observations
Most common formula — use this first.
Find Missing Number
Missing number = (Average × Total count) - Sum of known numbers
Very frequently asked in bank exams.
Average Speed
Average Speed = 2xy / (x + y)
Use when same distance covered at two different speeds x and y.
New Average after adding a number
New Average = (Old Sum + New Number) / New Count
When a new member joins a group.
⚡ Shortcut Tricks
#1
If average of n numbers is A, and a number x is added, new average = (n×A + x) / (n+1). No need to find sum!
#2
If all numbers increase by k, the average also increases by k.
#3
If average of first n natural numbers = (n+1)/2. Example: avg of 1 to 10 = 5.5
#4
Weighted Average trick: If group A has 'a' people with avg P, and group B has 'b' people with avg Q — combined avg = (aP + bQ)/(a+b).
#5
If a wrong number was used, correct average = old average + (correct - wrong)/n.