50 is exactly halfway between 40 and 60.
The number halfway between 18 and 60 is (18 + 60)/2 = 39.
60
65
It is: 70
(30+60)/2 = 45
59.5
40
It is: 45
60(40+80)/2 = 60
It is: (63+57)/2 = 60
The halfway point between 50 and 60 is (50 + 60) ÷ 2 = 55