Confusion Dividing A Fraction with a Whole Number... In the lesson I am doing, I divide fractions. Here is my problem:
28/55 / 7
I had to look up how to do this problem. According to Math Is Fun, you divide the denominator by the whole number and then simplify if possible. I did this, and got:
28/385
I couldn't simplify it, and the online quiz would only let me enter 2 digits in the denominator textbox. I couldn't figure it out, so I put in a random answer. They said it was:
4/55
How did they get this answer, and where did I go wrong? Please help, because I can't figure it out.

For a general purpose, suppose we need to find $y=\frac{\frac{a}{b}}{\frac{c}{d}}$ where $\frac{c}{d}\not=0.$ Then we can do the following - 
$$y\frac{c}{d}=\frac{a}{b}\implies \frac{c}{d}=\frac{\frac{a}{b}}{y}\\ \implies \frac{d}{c}=\frac{y}{\frac{a}{b}}\\ \implies y=\frac{d}{c} \times \frac{a}{b}.$$ 
For your problem, take $\frac{a}{b}=\frac{28}{55}$ and $\frac{c}{d}=\frac{7}{1}$.
