This is a very fun and motivating activity that can be done in 1 - 2 class periods, along with homework. It tells the story of an intern at a website who figures out a way to "hack" his burrito to almost twice the size by ordering "half-portions" of items like red and black beans, chicken and beef, and white and brown rice.
The activity looks at how hacking each ingredient adds to the weight of the burrito through the number of additional ounces and how those additional ounces can be written as percents. There are clear instructions for students on how to make the calculations.
The activity focuses on three uses of percents: the first is using percents to compare a part to a whole, as in "the addition of 3 ounces of beans made the burrito 15% heavier."
The second use of percents is "part to part." For example, if you went from having 3 ounces of beans in your burrito, and it increased to 5 ounces, what percent increase would that be?"
A third use of percents is also investigated: comparing percents to percents. For example, if your burrito was 16% cheese and salsa, and the new burrito went down to 8% cheese and salsa, did those ingredients go down by 8% (16% - 8%) or 50% (because 8% is half of 16%?)
There is also an application of proportions, as students calculate what the price of a "supersized" burrito should be if it was measured by the weight of the ingredients.
There are also questions included to get students thinking about the use of precision (does it matter if the size increased by 32.59% or is it easier to round off to 33%?) as well as place value, rounding and expressing decimals as percents.
This is a very relevant activity for your students and mine have enjoyed it immensely. It comes with complete teaching instructions and a detailed answer key.