6.NOS.1 Group 2 · Challenge

Practice Set · Part 1

Divide Mixed Numbers

Pick up where we left off

Name: Date: Group:

Where we left off

Our goal: I can divide mixed numbers by first changing them to improper fractions, explain why the method works, and use it on a problem I have not seen before.

The big idea: Always convert a mixed number to an improper fraction first, then divide using Keep, Change, Flip — and you can say why it is true, and where it would stop being true.

Model to copy — Watch me

  1. Agent Chen has a 3 1/2-mile route cut into 1/4-mile segments. I want 3 1/2 ÷ 1/4.
  2. First I convert 3 1/2. Multiply the whole by the bottom: 3 × 2 = 6. Add the top: 6 + 1 = 7. So 3 1/2 = 7/2.
  3. Now Keep, Change, Flip: keep 7/2, change ÷ to ×, flip 1/4 to 4/1.
  4. Multiply: 7/2 × 4/1 = 28/2.
  5. Simplify: 28/2 = 14. So 3 1/2 ÷ 1/4 = 14 segments.

Start here

You did these with your group. Now do them on your own — the model above is yours to copy.

  1. 1

    Same stepsFinish what the group started. Use the model above, step for step.

    Try it together — then prove it: Let's try 2 1/2 ÷ 1/2. First convert 2 1/2: 2 × 2 = 4, plus 1 = 5, so 2 1/2 = 5/2. Keep 5/2, change to ×, flip 1/2 to 2/1. Multiply: 5/2 × 2/1 = 10/2 = 5. So 2 1/2 ÷ 1/2 = 5. Now prove it: say why that move had to work at all — not just that it did.
    Show your work
  2. 2

    Warm restartWhat is the reciprocal of 3/5?

    1. A3/5
    2. B5/5
    3. C5/3
    4. D1/3

    How do you know?

  3. 3

    Warm restartWhat is 2/3 ÷ 1/3?

    1. A2/9
    2. B1/2
    3. C6
    4. D2

    How do you know?

  4. 4

    Warm restartWhat is 1/2 ÷ 1/4?

    1. A1/8
    2. B4
    3. C2
    4. D1/2

    How do you know?

6.10 Small Group · Group 2 · Practice SetPart 1 of 4
6.NOS.1 Group 2 · Challenge

Practice Set · Part 2

Divide Mixed Numbers

Keep going

You answered these out loud. Now write them.

Answer, then say how you know — the reason is the part that counts.

  1. 5

    Think it throughWrite 5 1/4 as an improper fraction.

    1. A21/4
    2. B51/4
    3. C9/4
    4. D20/4

    Why is that the answer?

  2. 6

    Think it through5 1/4 ÷ 3/4 = ?

    1. A7
    2. B4
    3. C6
    4. D3 3/4

    How do you know? Give a second reason as well.

  3. 7

    Think it throughCheck the answer: how long are 7 pieces of 3/4 foot?

    1. A5 1/4 feet
    2. B7 feet
    3. C3/4 foot
    4. D5 3/4 feet

    Explain your thinking. What would have to change for a different choice to be right?

  4. 8

    Back to the modelWhy is converting to an improper fraction the first step when dividing mixed numbers?

6.10 Small Group · Group 2 · Practice SetPart 2 of 4
6.NOS.1 Group 2 · Challenge

Practice Set · Part 3

Divide Mixed Numbers

Words and reasoning

Word bank · Banco de palabras

Divide Mixed Numbers (Dividir números mixtos)Mixed Number (Número mixto)Improper Fraction (Fracción impropia)Convert (Convertir)Simplify (Simplificar)Reciprocal (Recíproco)

Use the words

Fill each blank with a word from the bank.

Explain the thinking

  1. 9

    Find the mistakeAnother student made this exact mistake in this lesson. Explain why it is wrong, then write what they should have done.

    The mistake: A common mistake in Divide Mixed Numbers is dividing the whole-number parts and fraction parts separately instead of converting first — for example, treating 4 1/2 ÷ 1 1/2 as (4 ÷ 1) + (1/2 ÷ 1/2) = 5.
  2. 10

    Say moreWalk your partner through how you changed the mixed numbers before dividing.

  3. 11

    Write your ownWrite your own problem about this situation, then solve it and show the answer. The situation: Agent Chen maps a 3 1/2-mile suspect route and splits it into equal 1/4-mile segments so she can place a surveillance marker at each segment.

    Show your work
6.10 Small Group · Group 2 · Practice SetPart 3 of 4
6.NOS.1 Group 2 · Challenge

Practice Set · Part 4

Divide Mixed Numbers

Show what you know

Last check

These two come from Lesson 6.9. If they are shaky, that is the lesson to revisit — not this one.

  1. 12

    Show what you knowExplain your thinking — What is 2 2/3 ÷ 2/3?

    1. A4
    2. B2/3
    3. C8/3
    4. D1 7/9

    Explain your choice.

  2. 13

    From Lesson 6.9Explain your thinking — What is 9 ÷ 1/3?

    1. A27
    2. B3
    3. C9/3
    4. D1/27

    How do you know?

  3. 14

    From Lesson 6.9A student answered 2.5. What did they do wrong?

    1. AThey divided by 4 instead of by 1/4
    2. BThey multiplied by 4
    3. CThey added 1/4
    4. DThey used the wrong rope length

    How do you know?

Be honest — this tells your teacher what to do next

I can…Not yetGetting thereGot it
I can divide mixed numbers by first changing them to improper fractions, explain why the method works, and use it on a problem I have not seen before.
I can explain why it works: Always convert a mixed number to an improper fraction first, then divide using Keep, Change, Flip…
I can justify my answer to a skeptic and connect it to a second strategy or representation.

One question I want to ask my group next time