Question
If the arithmetic mean of x, x + 3, x + 6, x + 9 and x +
12 is 10, then x = ?Solution
ATQ,
We are given that the arithmetic mean of the numbers: x, x+3, x+6, x+9, x+12 is 10. To find the sum add all the numbers: x+(x+3)+(x+6)+(x+9)+(x+12) = 5x+(3+6+9+12) = 5x+30 By using the arithmetic mean formula:- 
So, 
Multiply both sides by 5: 5x+30 = 50 Subtract 30: 5x = 20 ⇒ x= 4
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