is 3.10723 rational

Yes, it is a rational number; decimal.

Yes it is rational. 

This is because it can be expressed as a fraction 3.10723 is also 3 10723/100000

note: not all decimals are rational, pi is an example of an irrational decimal.

A decimal is rational if it terminates or if it repeats indefinitely. The decimal fits the first condition and is, therefore, rational.