Find a rational number exactly halfway between:
(a) -1/3 and 1/3
(b) 1/6 and 1/9
(c) 5/-13 and -7/9
(d) 1/15 and 1/12
(a) 0
(b) 5/36
(c) -136/234
(d) 3/40
Halfway = average of two numbers = (a+b)/2.