Chef Matthew served a rice and sauce dish by mixing already

Sure! You're welcome, S1937.

I do recommend using the weighted average mapping strategy (I've also seen it called the "tug of war" or "teeter-totter" approach) for weighted average and mixture problems, because it will save you time over doing the algebra. In fact, this approach is just a shortcut for the algebra, allowing you to go straight to finding the ratio between the weights. However, in order to be able to feel comfortable using this strategy, you will need to practice it. I have a list of Official Guide and Veritas Prep questions that you can use to practice the weighted average mapping strategy at the following link:

Weighted Average Mapping Strategy practice questions

The only time when the weighted average mapping strategy won't work well is when the ratio between the weights is messy. In the vast majority of weighted average and mixture problems, including this one, the ratio is nice, so it works well.

If you wanted to just do the math without the weighted average mapping strategy, you could use 2 and 3 as the amounts of pecov in the rice and sauce, then use the percentages of non-liquid pecov (15% and 70%) to calculate the total non-liquid pecov:

2*0.15 + 3*0.7 = 0.3 + 2.1 = 2.4

Then divide that by the total amount of pecov (2+3 = 5) to get the overall percent of non-liquid pecov:

2.4/5 = 48%

However, I think that the weighted average mapping strategy is faster, if you are comfortable with it. Please let me know if you have more questions about this!