An actual maths examination doesn't get any easier if you have a calculator.
For a start, it rarely involves many numbers. If you're at an intermediate stage all it will allow you to do is skip the chore-work of, for example multiplying all the elements of two matrices by hand. Not that you shouldn't be able to do that if needed, but it's at a level so far below that which you're actually testing that to enforce it only serves to make maths feel even less appealing to those who are not inclined to love it.
If you're testing arithmetic on the other hand, calculators are right out.