The average of 8 numbers is 45. If each number is decreased by 3, what will the new average be?
- AOption (a)
42
- BOption (b)
39
- COption (c)
45
- DOption (d)
8
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Correct answer
42
Why this answer is correct
Shortcut Trick
If each number in a set is decreased by a constant value k, the average of the set also decreases by the same value k.
Given Old Average = 45 and Decrease per number = 3.
New Average = 45 − 3 = 42.
∴ The correct answer is 42.
Alternate Method
Given:
Total numbers = 8
Initial Average = 45
Formula Used:
Average = Sum of observations ÷ Number of observations
Calculations:
⇒ Initial Sum = Average × Count = 45 × 8 = 360
⇒ Total Reduction = 8 × 3 = 24
⇒ New Sum = 360 − 24 = 336
⇒ New Average = 336 ÷ 8
⇒ New Average = 42
∴ The correct answer is 42.
Additional Information
Addition Rule
If k is added to every observation, the new average is Old Average + k.
Multiplication Rule
If every observation is multiplied by a constant n, the new average becomes Old Average × n.
Division Rule
If every observation is divided by a non-zero constant m, the new average is Old Average ÷ m.