Question

The mean of this data set is 9. What number is missing?

11,20,_,3,1

Answer 1

Let the missing number be x

Mean is the total sum of data over the number of data therefore,

(11+20+x+3+1) / 5 = 9
Then simplify
(35 + x) / 5 = 9
Then multiply 5 to both sides
35 + x = 45
Then subtract 35 to both sides to find x
X= 10

Hope this helps!