Check the manual of your specific calculator. What I have seen is usually something like the following: The calculator tends to automatically show fractions as mixed fractions. The calculator has a "fraction" key, often labelled ab/c. Pressing the "shift" key (or some similar key for "extra functions") followed by the fraction key will often to the desired conversion in the other way (from mixed to improper).
You change them into improper or topheavy fractions.
Change them to improper fractions and double them.
Change them into mixed numbers and add the integers and fractions together ensuring that the fractions have a common denominator.
Some numbers are improper fractions and some are not. For example, 1/2 or 0.5 is a number but not an improper fraction. And there is no way in which you can express it as an improper fraction.
That's a proper fraction. Fractions can be either proper or improper and can't change.
You change them into improper or topheavy fractions.
Change them to improper fractions and double them.
You cannot.
For addition, subtraction, division and multiplication with other fractions
Change them into mixed numbers and add the integers and fractions together ensuring that the fractions have a common denominator.
4.09 as an improper fraction is 409/100
Convert them to improper fractions and proceed the same way you would multiply two fractions.
improper fraction
If your calculator is a scientific one then just press the S<=>D button
improper fraction
improper fraction
an improper fraction