Modeling Decimal Division

Strategies to Divide Decimals

Unit Test Review

by Mr. Lasaitis

Multiple Choice

Hugo wants a dirt bike! He buys one for $2,349.89. He will pay for the bike by paying the same amount each month for 12 months. What is the best estimate for how much he will pay each month? *Hint: this is a great time for a compatible number. What are the multiples of 12?

• $100 

   

• $250

• $200

• $300

​Explanation

​We could estimate the answer by rounding from 2349 up to 2500 and by rounding 12 down to 10, but in this situation, using a compatible number will be closer to the actual answer, and potentially faster to calculate.

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​ Since 24 is a multiple of 12 and 2349 is very close to 2400, we can use that to give us a very close estimate of $200

Multiple Choice

Use number sense about decimal placement to complete the equation. What are the correct divisors for A, B and C? The choices are 0.12, 1.2 and 12.

$$54.36\ \div\ A\ =\ 45.3$$   $$543.6\ \div B=4,530$$   $$5.436\div C=0.453$$  

• A=12

  B=1.2

  C=0.12

• A=1.2

  B=1.2

  C=12

• A=1.2

  B=12

  C=0.12

• A=1.2

  B=0.12

  C=12

​Explanation

​Number sense requires us to think about math in a different way. It can make more sense to think about these types of questions using at least 1 number that is familiar to us, like 1, 10 or multiples of ten.

​

​Watch the video for an explanation.

Multiple Choice

Find the better deal! Julianne can buy 9.25 ounces of Doritos for $3.33, or she can buy 15.5 ounces for $4.65. Which of the following explains which is a better deal? Hint* You need to find the price per ounce, by dividing, for each size and compare the answers.

• The smaller bag is the better deal, because it costs $0.04 less per ounce than the larger bag.

• The smaller bag is the better deal, because it costs $0.06 less per ounce than the larger bag.

• The larger bag is the better deal, because it costs $0.04 less per ounce than the smaller bag.

• The larger bag is the better deal, because it costs $0.06 less per ounce than the smaller bag.

​Explanation

​This happens all the time! First we need to divide to find the cost per ounce for each size of chips. Since it is a cost per ounce we should divide cost by ounces.

Small bag = $3.33/9.25 = $0.36 per ounce

Larger bag = $4.65/15.5 = $0.30 per ounce

​Then compare 0.30 < 0.36 so the larger bag costs less per ounce and is a better deal.

Open Ended

Amari solved the problem 136.4 ÷ 22 = 6.2

Complete the model with partial products to check Amari’s work with multiplication. Solve for each letter.

​Explanation

Since Amari already did the division, we can use multiplication to check his answer. In this case we will use partial products. Don't let the area model trick you, we just need to multiply to fill in the area size for each letter. A = 20x6, B=0.2x20, C=6x2, D=0.2x2