Review 1: Eating Out at the Hamburger Hut - Working with Decimals

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Objective

SWBAT add and subtract decimals, multiply and divide decimals, determine whether to add, subtract, multiply or divide to solve a word problem.

Big Idea

In this lesson, students will review the procedures involved in calculating with decimals and they will have to apply that knowledge to answer questions about eating at a restaurant.

Do Now

5 minutes

See the Do Now video in my Strategy Folder for more details about how I begin class.  Often, I create do nows that have problems that connect to the task that students will be working on that day.  For this do now, I picked to multiple choice problems from my released state test.  Percents and working with integers were two skills I identified that students need more practice with. 

While checking question 1 I tell students I believe the answer is C 15%.  I ask students to respond to my answer.  Then I ask students “What does a percent represent?”  I am looking for students to express that a percent is a ratio out of 100.  For question 2, I ask students “What does it mean if a temperature is negative?”  I am looking for students to share that a negative temperature is less than zero.  I want students to be able to express that a negative temperature is colder than a positive temperature. 

 

Decimal Operation Review

12 minutes

After the Do Now, I have a student read the objectives for the day.  I will ask students to share out why it is important to be able to accurately calculate using decimals.  There are so many connections with money and measurement that students can make.  I tell students we will do a review of procedures when calculating with decimals and then they will use a restaurant menu to answer questions.

On page 3 we work through rules and examples together.  I include addition and subtraction problems where students must fill in missing place values and regroup.  A common mistake a see struggling students do is lining up the numbers instead of the place values.  For instance, a student set up the subtraction problem as 59.03 – 72.5 because 59.03 had more digits.  I write that example on the board and have students respond to it.  I remind students that they must use their number sense!  You know an amount close to $72 is greater than an amount close to $59, therefore the amount close to $72 must be the top number in your stack.

The multiplication problem (4.3 x .56) is a great opportunity to talk about different ways to find this product.  This discussion gets students engaging with MP3: Construct viable arguments and critique the reasoning of others and MP8: Look for and express regularity in repeated reasoning.  Questions I may ask students:

  • Is multiplying 4.3 x .56 the same as multiplying 4.30 x .56?  Why or why not?
  • Does this always work?  Come up with a similar example that supports your idea.
  • What connections can you make to equivalent fractions? (3/10 is equivalent to 30/100)?
  • Is one way more efficient?  Why or why not? 

For the division example, students who struggle with division may come up with the quotient 9.8 instead of 9.08.  I go through this example together and have students explain the step by step procedure.  These students forget that if the divisor cannot be divided into the part of the dividend that they must first put a zero in the quotient before bringing down the next digit of the dividend.    Students sometimes struggle with lining up the quotient correctly and then place the decimal point incorrectly.  I encourage students to look at each answer and ask themselves, “Does my answer make sense?”  I think aloud that 136.2 isn’t that far from 150 and I know that 15 x 10 = 150, so my answer should be close to 10.  I ask, “Should my answer be greater than or less than 10?”  I want students to continue to develop their number sense and estimation skills.

 

Operation Practice + Independent Practice

23 minutes

After completing page 3 together, students complete the problems on page 4 independently.  I am circulating to check students work when they are finish.  I only let students move on to the restaurant menu problems when they have correctly answered the 4 problems. 

During independent practice I am circulating to see what strategies students are using and what struggles they are having.  On number 4 on page 6 I look for whether students found a total and then subtracted it from $10, or whether they just calculated a total.  I am also looking to see if they added decimal places to $10 so that they could subtract.

Extension: If students complete the problems, tell them that they have $20 for them and a friend to go out for a meal and pay the tip.  Ask them to list what they will order, find a total, and calculate a 20% tip.  How much money will they have left?

Closure

10 minutes