Math Application - Teaching Strategies
Students will use the information learned in this unit to deepen their understanding of percents as well as compute percents and calculate percent increase and decrease.
The Human Body
Table 1: Percentage of Elements Found in the Human Body, will be used to help students understand the concept of 100%. I will give students a version of the table that does not have the elements in order. They will compare and order the elements from greatest to least. This will give students practice in ordering the percents that contain a decimal. Many students struggle to understand that 0.12% is less than 0.5%. Place value will be addressed at this point in time. With additional activities and discussions about the quantity of the elements I hope students will begin to understand the values.
Once students have compared and ordered the elements on the table they will then add the percentages to see that altogether it creates 100%. Students will use their body weight to calculate the weight of each element in their own body. For example, a student weighing 120 pounds would find the weight of oxygen in his or her body by multiplying 120 x .65 = 78. The students will continue finding the weight of each element. Some elements will require students to multiply correctly using decimals. The same 120 pound student will calculate the iron weight by multiplying 120 x .006 = 0.72. Once students finish calculating the weights of all the elements in their bodies they will add those weights up to hopefully get 100% of their body weight. This will be challenging for students because errors are made consistently when adding numbers with decimals. Many students forget to line up decimals when doing the addition. They usually don't pay much attention to the error. On a decimal worksheet the idea of a "reasonable answer" never crosses their minds. In this situation, I would imagine a student weighing 120 pounds is going to see a red flag if the total weight turns out to be in the thousands!
Vitamin C Recommendations
The metric system is a foreign concept to most 7 th grade students. They are not familiar with conversions and therefore Klenner's recommendation of 350 mg per 1 kg of body weight doesn't phase them. In order to help students understand Klenner's recommendations, students will convert their weight into kilograms. Students will calculate the recommendation for their weight. Using salt as a substitute for vitamin C, students will weigh the amount recommended by Klenner. They will compare that amount to the RDA for vitamin C. This will give students more exposure to the metric system as well as some fascination with Klenner's recommendations.
Supplement Facts
Multi-vitamins are a popular way for people to get their daily dose of vitamins and minerals. The serving information is a great way for students to practice calculating percents. The label for most vitamin supplements includes the vitamin, the amount, and the percent of the Recommended Daily Intake (RDI). It is interesting that in the multi-vitamin some quantities are below the RDI at 20% and other quantities are far over the RDI at 300%. Students will be able to use the serving information to calculate the amount and serving size to obtain exactly 100% of the RDI. Proportions are one method students are taught to solve percent problems. This information will work well using that method. Again, this will give students an opportunity to look at the "reasonable answer". For example, 1 multivitamin contains 150 mcg Biotin, which is 50% of the RDI. Students would calculate the number of servings (2) and amount (300 mcg) necessary to receive 100% of the RDI. Students who invert the numbers and get a solution like ½ a serving and 75 mcg would be able to re-think the solution in context. If a pill gives you 50% what you need, does it make sense to only take ½ of the pill? These questions will be more challenging when the serving gives over 100%. For example, Vitamin B6 5mg is 250% of the RDI. Students who calculate the serving size (2/5 or 0.4) will also be able to work with the conversion of fractions and decimals.
Percent Increase and Decrease
"Which number goes where?" Students are phenomenal at memorizing the process. This is because that is often what they are taught. This issue becomes a nightmare when it is time for students to learn percent change. If this topic is taught out of context students have no option other than to memorize a formula. They are great at setting up the formula but are never sure how to fill in the numbers. In context, it is clear, and students capable of solving percent problems will easily be able to apply those skills to percent increase and decrease.
The Council for Responsible Nutrition provides two great resources for learning about percent change. The first table entitled, Comparison of Current RDIs, New DRIs, and ULs for Vitamins 24 shows the dosages for the different recommendations. The second, Historical Comparison of RDIs, RDAs, and DRIs, 1968 to present for Vitamins 25 shows the change of dosage for each recommendation over time. Both tables give valuable data for students to calculate the percent change of the dosages. Graphing the data from the tables is valuable so students can see what percent change looks like on a graph. The idea is to give students a broad understanding and help them internalize the concept.
I have never taught a math unit focused on a science topic. I look forward to seeing my students engage in this unit and learn percents in an applicable way.
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