Question

Can you ever use a calculator to determine if a number is rational or irrational? Explain.

Answer 1

irrational cannot be represented as a fraction. so your answer is yes.

Answer 2

I would say no' as calculators were designed to give us approximate answers when dealing with irrational numbers.
It would be hard to guess whether a large number produced by a calculator is irrational or not given that fact that many rational numbers can be incredibly long.