Bank Exam Speed Maths
Page 7: Average (Shortcut Methods)
1. Average Basics
Average = Total Sum / Number of Items
Example: Average of 10, 20, 30
= (10 + 20 + 30) / 3 = 60 / 3 = 20
= (10 + 20 + 30) / 3 = 60 / 3 = 20
2. Shortcut Method
Total = Average × Number of Items
Example: Average = 25, Items = 4
Total = 25 × 4 = 100
Total = 25 × 4 = 100
3. Replacement Concept (Important Trick)
When one value is replaced:
Change in Average = (New Value - Old Value) / Total Items
Example:
Average of 5 numbers = 20
One number 30 replaced by 50
Increase = (50 - 30)/5 = 4
New average = 20 + 4 = 24
Average of 5 numbers = 20
One number 30 replaced by 50
Increase = (50 - 30)/5 = 4
New average = 20 + 4 = 24
4. Combined Average
Formula:
(Sum1 + Sum2) / (Total Items)
(Sum1 + Sum2) / (Total Items)
Example:
Group A avg = 20 (5 people)
Group B avg = 30 (5 people)
Combined avg = (100 + 150)/10 = 25
Group A avg = 20 (5 people)
Group B avg = 30 (5 people)
Combined avg = (100 + 150)/10 = 25
5. Important Tricks
• If all numbers are equal → Average = same number
• Average lies between smallest and largest value
• Use total method instead of direct calculation
6. Practice Questions
1. Find average of 5, 10, 15, 20
2. Average = 30, Items = 6 → Total = ?
3. One value 40 replaced by 60 in 5 items → New average?
4. Avg of two groups: 10 (4 items), 20 (6 items) → Combined avg?
5. If all values are 25, what is average?
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