Which pair of ratios form a proportion? My daughter is stuck on this question and we're not sure what the answer is. I'm rusty with math skills, so I don't understand how to help her, or what approaches she's tried. Please help us!
10.5/12 and 2/5
13/7 and 7/13
9/30 and 1.5/5
7/5 and 10/8

They are asking which pair of fractions are equal. To check this, you will need to convert the fractions so that they have a common denominator.
Here is an example of getting a common denominator for the first pair of fractions (recall that multiplying by fractions like $\frac{7}{7}$ or $\frac{12}{12}$ does not change a number's value since these are equal to $1$):
$$\frac{10.5}{12} \stackrel{?}{=} \frac{2}{5}$$
$$\frac{10.5}{12} \times \frac{5}{5} \stackrel{?}{=} \frac{2}{5} \times \frac{12}{12}$$
$$\frac{52.5}{60} \neq \frac{24}{60}$$
Now it is obvious that these two fractions are not the same.
Another example:
$$\frac{9}{30} \stackrel{?}{=} \frac{1.5}{6}$$
$$\frac{9}{30} \times \frac{6}{6} \stackrel{?}{=} \frac{1.5}{6} \times \frac{30}{30}$$
$$\frac{45}{180} = \frac{45}{180}$$
Here the fractions are indeed equal.

As Barry mentioned, you can use the shortcut to check if $ad \stackrel{?}{=} bc$ since this amounts to checking if the numerators are the same after the denominators have been made equal.
