Thursday, December 5, 2013

Real World Math: Dividing Decimals

I have decided to start writing posts about how you can incorporate real world skills into your math class, depending on what standard you are working on.  One major aspect of really providing rigorous learning for your students is to take the everyday skills you teach, and connect them to something useful in the outside world so that they will understand why they are learning them and how they may use them in their future.

This week we finally moved into decimal division.  I like to begin this with whole numbers in the divisor.  In this case, students simply move the decimal from the dividend straight up into their quotient.  Next, I like to move on to decimal division with whole number divisors that do not evenly divide, so my students have to learn the concept of adding zeroes to the dividend to continue dividing.  Third, I have them divide two whole number, the smaller number being the dividend so that they learn the skill of adding a decimal and zero to the dividend.  Finally, we finish up with dividing a decimal by a decimal.  Having a decimal in the divisor is incredibly tricky, especially in Common Core.  They must learn the concept of multiplying the dividend and divisor by the same power of ten, until the divisor becomes a whole number.  This is very difficult for students to grasp.  The easiest thing to do is to just tell them that they need to move the decimal to the right in the divisor until it becomes whole, and then move the decimal in the dividend the same number of places.  Unfortunately, teaching the trick is no longer a best practice, and it is important for students to understand WHY they are solving problems in the way that they are.

Sounds confusing, right?  Try teaching it!  I have yet to find a truly groundbreaking way to teach decimal division, but I am definitely working on having my students practice with real-life examples.  Here are some life skills that you can incorporate into your lessons:

Dividing Decimals by Whole Numbers

  • Provide your students with restaurant bills and have them decide how much each person would owe if it was split evenly.
  • Create a yearly salary for your student and have them figure out what their monthly income would be.
  • Create an amount of some type of cupcake mix that has to be split up evenly into 12 or 24 cupcakes.  Determine how much batter will be needed for each cupcake

Dividing a Smaller Whole Number by a Larger Whole Number

  • Have students find the batting averages of baseball players - divide the number of hits by the number of times at bat (you can include real examples from professionals).  For example:  Derek Jeter had 56 at bats in his last 25 game.  If he had 28 hits, what is his batting average?

Dividing a Decimal by a Decimal

  • Take an amount of food, and divide it up into portions that weigh a certain number of pounds, ounces, grams, etc. (that isn't a whole number)  For example:  I had 25.2 ounces of cupcake batters to separate.  If each cupcake gets 1.2 ounces, how many cupcakes I you make?

If you have other examples of real world problems that can be used for dividing decimals, please reply below.  I would love to continue adding them to this post so that you can incorporate them into your lessons.

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