Question

What is the missing number in the data set 15,17,28,30 if the mean is 23

Answer 1

15+17+28+30=90, if theres another number than there r 5 total numbers, 23*5=115, 115-90=25, so 25

Answer 2

mean is add the numbers and divide the result by how many numbers there are
mean=23
1 missing number which is x
5 numbers including missing one
(15+17+28+30+x)/5=23
solve for x
multiply both sides by 5
15+17+28+30+x=115
add like terms
90+x=115
subtract 90
x=25

the missing number is 25