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: Multiply 0.4 × 0.7. Multiply 4 × 7. Then count the decimal places in both factors. (4 × 7 = 28, and 1 + 1 = 2 places) Place the point. What is the product? (0.28) Why is 0.28 smaller than both 0.4 and 0.7? (Both factors are less than 1. Multiplying by a number less than 1 takes only part of the other number.)

   Show your work
2. 2

   Warm restartWhat is 3.2 + 4.5?

   1. A7.5
   2. B7.7
   3. C8.7
   4. D77

   How do you know?
3. 3

   Warm restartWhat is 14.6 + 3.85?

   1. A17.45
   2. B18.35
   3. C18.45
   4. D18.55

   How do you know?
4. 4

   Warm restartWhat is 20.3 − 7.48?

   1. A12.18
   2. B12.82
   3. C12.92
   4. D13.82

   How do you know?

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 through3.5 × $6.80 = ?

   1. A$2.38
   2. B$21.80
   3. C$23.80
   4. D$238.00

   Why is that the answer?
2. 6

   Think it throughRound to estimate: about how much should the deli meat cost?

   1. Aabout $2.80
   2. Babout $14
   3. Cabout $28
   4. Dabout $280

   How do you know? Give a second reason as well.
3. 7

   Think it throughA student answered $238.00. What went wrong?

   1. AThey added instead of multiplying
   2. BThey rounded too early
   3. CThey used the wrong price
   4. DThey put the decimal point in the wrong place

   Explain your thinking. What would have to change for a different choice to be right?
4. 8

   Back to the modelHow did estimating by rounding help you sort the products? How do you decide where to place the decimal in the exact product?

Use the words

Fill each blank with a word from the bank.

• The answer to a multiplication problem is the ___.
• The dot that separates whole numbers from parts of a whole is the ___.
• Finding an answer that is close but not exact, to check if a product is reasonable, is to ___.
• The value a digit has based on its position is its ___.

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 Multiply Decimals is counting decimal places from only one factor instead of adding the decimal places from BOTH factors.
2. 10

   Say moreWhen you multiplied 4.5 × 12.60, how did you decide where to put the decimal point in the product?
3. 11

   Write your ownWrite your own problem about this situation, then solve it and show the answer. The situation: The station needs 4.5 meters of heat shielding. The shielding costs $12.60 per meter.

   Show your work

Last check

These two come from Lesson 2.11. If they are shaky, that is the lesson to revisit — not this one.

1. 12

   Show what you knowExplain your thinking — What is 4.6 × 2.3?

   1. A1.058
   2. B10.48
   3. C10.58
   4. D105.8

   Explain your choice.
2. 13

   From Lesson 2.11Explain your thinking — What is 32.6 − 14.85?

   1. A17.25
   2. B17.75
   3. C17.85
   4. D18.75

   How do you know?
3. 14

   From Lesson 2.11Did she beat her personal record of 7.5 minutes?

   1. ANo, because 7.43 > 7.5
   2. BYes, because 7.43 < 7.5
   3. CNo, because 7.43 and 7.5 are equal
   4. DYou cannot compare them

   How do you know?

Be honest — this tells your teacher what to do next