Answer: in the 3 pairs we can find a rational number.
Explanation:
A rational number can be any number written as a quotient of two integers.
The rational numbers have a finite number of decimals after the point (or periodic)
a) (-10, -9)
between those two numbers we have, for example, -9.5
and we can write this as:
-9.5 = 95/100
b) (5.91, 5.92)
between these numbers, we have the number 5.915
and we can write it as: 5.915 = 5915/1000
c) (2/3, 4/5)
between 2/3 and 4/5 we have for example the number 3/4.
because 2/3 = 0.66....
4/5 = 0.80
a number between those two is 0.75 = 3/4.