Multiplying Decimals by Whole Numbers

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SWBAT multiply decimals by whole numbers.

Big Idea

Multiplying decimals is a life skilled used in purchasing goods, cooking, and spending money.


15 minutes

Students will be completing a memory box.  Give them a few minutes to look over their notes from adding and subtracting decimals.  Once their time is up, have them close their notes and write down everything they remember about adding and subtracting decimals in their memory box. Encourage students to use visuals, words , or examples in their memory box.  When students are finished, have the do a HUSUPU and share the information from their memory box.

Memory box supports mathematical practices 1, 3, and 7

Multiplying decimals by whole numbers (teacher directed)

20 minutes

The purpose here is to get the students to see the algorithm used to multiply decimals by whole numbers.  For each problem, I will have the students estimating what their answer will be.  This is especially helpful when the decimal is less that one.  Students often get confused as to why their answer is so small when multiplying with decimals less than one.  Estimating helps students realize this notion.  I will be setting up each problem and modeling, out loud, how I’m doing the steps.  When it comes down to finding where to put the decimal, I’m going to ask the students to look at their estimate and see if they can figure out where the decimal should be placed.  In the end, I’m going to ask them if they notice a pattern between the numbers in the problem and the placement of the decimal (SMP 6 and 8)

Multiplying decimals by whole numbers (student's try)

20 minutes

Have the student use white boards and markers to work out each problem.  Students should estimate their answer first, then do the computation to find the solution.  Students can check with table mates before they show you the answer on their white boards.  I always tell them that when I say “whiteboards up” then they should put their boards up so I can check all at once.  As students show their answers, be sure to ask how they knew where to place the decimal.  

Around the Room

20 minutes

Students will be completing an Around the room.  There are 10 problems and each problem deals with money and the purchasing of multiple amounts.  I liked this because it shows the students where we use this in real life.  


10 minutes

Students will be completing a comprehension menu for multiplying with decimals.  Students should work out all 4 problems and put a mark in the box they found the easiest to answer. The comprehension menu checks for 4 types of understanding:  mastery, understanding, self-expressive, and interpersonal.  Each box will support the same concept, but with different types and levels of understanding.  Comprehension menu supports mathematical practices 1,2,3,5.  Students should turn their comprehension menu in so you can assess learning.