Question

When would it be logical to use `22/7` instead of `3.14` for pi?

Answer 1

It's just the matter of preference for you.

Explanation:

If you see in your problem that there are a lot of fractions, then you can go ahead and use `22/7` so that you could cancel some terms out and simplify your calculations.

But if you see in your problem that there are decimals and whole numbers you can go ahead and use `3.14`.

But again, it's just a matter of preference. You could also write,
`3.14 = 314/100`.

The goal mainly is to simplify your calculations and make it easier for you to carry on the arithmetic or algebraic operations. The only logic is to see which will benefit you the most and save your time while solving a particular problem.