I have a test tomorrow, and was given examples of the types of problems that I'd be taking. I figured everything out, except this one.

A student misses 5 of her 31 classes in a semester. What is her attendance percentage?

26/31 x 100 = __%

This seems ridiculously easy, but during the test, calculators are forbidden. So I can't just type in 26/31 and be done. I looked up methods to manually convert fractions to decimals, but the only one I found works like this:

Say I'm converting 3/4. I need to find a way to make the denominator (4) into a number divisible by 10. In this case, that would mean multiply by 25. Now I multiply 3/4 by 25/25, and get 75/100. Therefore, .75 would be the decimal form.

This works fine...but only for certain numbers. 31? I got to the billions trying to find a working number, and got nothing. Considering that the test is timed, and I don't want to have to manually check 10-100-1000-10000-100000-1000000-10000000 etc. etc. etc. for whatever denominator I get. So...is there another way? Or am I stuck with the 10-divisible number theorem?

Help is appreciated