I'd say 100 even, don't know if this is a real question or not.
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!
1. It's a proportion...50 over 12.5 = h over 50 then cross multiply and divide
2. Another proportion 7over x = 2 over 6 then cross multiply and divide
