Let's define the total amount of time Grace spent doing homework as $T$ minutes. According to the problem, Grace spent 15 minutes on her math homework, which was 30% of the total time spent on all her homework.

To represent this relationship, we can set up the following equation: $15 = 0.30 \times T$

Now, solve for $T$:

$T = \frac{15}{0.30} = 50$

So, Grace spent a total of 50 minutes on her homework.

Would you like more details or have any questions?

Here are five related questions to explore:

1. If Grace spent 20% of her homework time on science, how many minutes did she spend on science?
2. How many more minutes did Grace spend on other subjects compared to math?
3. If Grace spent an equal amount of time on 3 different subjects (excluding math), how long did she spend on each?
4. What percentage of Grace's homework time did she spend on non-math subjects?
5. If Grace spent 45% of her homework time on English, how many minutes did that take?

Tip: When solving percentage problems, it can be helpful to first translate percentages into decimals by dividing by 100!