The answer is 1414
Then number half way between them is their mean average: (-3/7 + -15/14) ÷ 2 = (-6/14 + -15/14) ÷ 2 = -21/14 ÷ 2= -21/28 = -3/4
21
34
(21 + 69)/2 = 90/2 = 45
The answer is 1414
19.5 is halfway between 18 and 21
Then number half way between them is their mean average: (-3/7 + -15/14) ÷ 2 = (-6/14 + -15/14) ÷ 2 = -21/14 ÷ 2= -21/28 = -3/4
21
It is: (18+21)/2 = 19.5
42
34
There is no "the" rational" number since there is an infinity of them. Start with the number halfway between the two: (1/10+1/11)/2 = 21/220. Then try halfway between 1/10 and 21/220, and then halfway between 1/10 and that on. And so on.
(21 + 69)/2 = 90/2 = 45
(21+29)/2 = 50/2 = 25
seventeen 13 + 4 = 17 = 21 - 4
14