Question

The mean of a set of x numbers is 17. When 3x is added to that data set, the new mean is 18. Find x.

Answer 1

S/x = 17 ----> S = 17x


(S+3x)/(x+1) = 18


(17x+3x)/(x+1) = 18


(20x)/(x+1) = 18


20x = 18(x+1)


20x = 18x+18


20x - 18x = 18


2x = 18


x = 18/2


x = 9

Answer 2

Thanks jim. Makes sense.

Answer 3

You're welcome

Answer 4

since mean of x numbers is 17
=> Sum of x numbers = 17x
we add one more number i.e. 3x so now the numbers are (x + 1)
and sum of (x + 1) = 17x + 3x = 20x

20x
so mean of (x + 1) numbers = ------
x + 1

ATQ,

20x
----- = 18 => 20x = 18(x + 1) => 20x = 18x + 18 => 20x - 18x = 18
x + 1

=> 2x = 18 => x = 18/2 => x = 9