Enthuware

Is there an error with this question?

The solution shows 'double or float' and the explanation gives 'int,long,float or double'

Yes, it is correct because it does not say only double or float.

I was expecting that when giving the amount a type of float or double the real result would be given.
So 0,8. But it gives 1.0 as a result.
Only declaring rate as a float/double of casting the rate within the expression to float/double will give the real result.
I don't understand why this is.

If you have only int variables in a term, then integer operation is performed for that term. For example, in the term rate/100*1, all are ints. Therefore, it will actually return 0. If you do ((double)rate)/100*1, now you have a double in the term, so everything in that term will be promoted to a double and it will return .9.

Strange that they implemented it that way, but now I know I can use it the right way.