Students who don't "get" other aspects of math often "get" percents. They have gone shopping with their parents, they know what a 30% off sale is, and come into class at the beginning of our percents unit knowing what percents are. The key is to grab and hold their attention.
I begin my percents unit with an activity that is designed to figure out if students can calculate percents of different wholes while building an understanding that if the whole changes, the part will change accordingly. Essentially, when x>y, p% of x>p% of y. This has halachic implications, based on the pasuk I quoted above.
The pasuk in this week's parsha is brought as the source for the prohibition of separating Trumot and Maasrot (tithes) out of order. Rabbi Jack Abramowitz explains in The Taryag Companion, "The tithes are a percentage of the whole, a percentage of the remainder, etc. Going out of order invariably leads to errors in one’s calculations."
I designed an activity based on one we did when I was in school, where we imagine a scenario with 10,000 bushels of wheat. Presuming Trumah is 1/50th of the harvest (it can range from 1/40th-1/60th, but 1/50 is 2% and easy to calculate), how many bushels of wheat will the Kohen, the Levi and the Ani get? (In years 3 and 6, of course.)
If we do the math right, Joe Kohen, Yoni Levi and Shani Ani get 180, 980 and 882 bushels respectively. If we change the order and give one person before his or her turn, the ones who come later may not get what they rightfully deserve. Check out the worksheet here and the answer key here.
Kids like the exploration style of this lesson and usually find calculating bushels of wheat to be novel. (After all, we don't do this every day.) This lesson goes over well, year after year.
I always tell my students about the Taryag concept: everyone agrees there are 613 core mitzvot but not everyone agrees what counts as a mitzvah. This law is not the law of Maaser and Terumah itself, it is a supplemental law about how to do the mitzvah itself, which teaches means that each of these laws is really two Biblical laws (or more!) Tithes might not be such a popular topic of conversation, but when the Rabbis double count a law, they do so to show us values and priorities - Maaser teaches us about the responsibility we have for other people in the community, and our law teaches us how important it is to be precise in our financial dealings with other people.
Updated 2/1/16 at 12:24pm to correct an error in the answer key.
