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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 add 12.45 and 7.8. First, how do we write 7.8 with two decimal places? (7.80.) Line up the points and add the hundredths, then tenths, then ones. What do we get? (12.45 + 7.80 = 20.25.) So the sum is 20.25. The points stay lined up in the answer. Now prove it: say why that move had to work at all — not just that it did.

   Show your work
2. 2

   Warm restartA data set has one very large outlier. Which measure of centre does it pull on MORE?

   1. AThe mean
   2. BThe median
   3. CNeither one
   4. DBoth equally

   How do you know?
3. 3

   Warm restartHouse prices on a street are $180,000, $190,000, $200,000, $210,000 and $2,000,000. Which measure best describes a typical price?

   1. AThe median
   2. BThe mean
   3. CThe range
   4. DThe largest value

   How do you know?
4. 4

   Warm restartA data set is roughly symmetric with no outliers. Which measure of centre is a good choice?

   1. AThe mean
   2. BThe range
   3. COnly the maximum
   4. DNeither the mean nor the median

   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 through2.45 + 2.60 + 2.38 = ?

   1. A7.43
   2. B7.143
   3. C6.43
   4. D7.53

   Why is that the answer?
2. 6

   Think it throughWhy is it safe to rewrite 2.6 as 2.60?

   1. AAdding a zero at the end of a decimal does not change its value
   2. BIt makes the number ten times bigger
   3. CIt rounds the number up
   4. DBecause 6 and 60 use the same digit

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

   Think it throughDid she beat her personal record of 7.5 minutes?

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

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

   Back to the modelHow does a number line help you see what happens when you add or subtract decimals?

Use the words

Fill each blank with a word from the bank.

• Line up equal ___ ___ before you add or subtract decimals.
• A number that uses a point to show a value less than one whole is a ___.
• The value a digit has based on its position in a number is its ___.
• The first place to the right of the decimal point is the ___ place.

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 Add and Subtract Decimals is lining up the last digits (the right edges) of each number instead of lining up the decimal points — for example, adding 8.
2. 10

   Say moreWhen you added 128.75 and 46.8, how did you handle 46.8 having fewer decimal places, and when did you need to regroup?
3. 11

   Write your ownWrite your own problem about this situation, then solve it and show the answer. The situation: The space station's fuel tank reads 128.75 liters. A resupply shuttle delivers 46.8 liters, and then the docking thrusters burn 19.35 liters.

   Show your work

Last check

These two come from Lesson 2.10. If they are shaky, that is the lesson to revisit — not this one.

1. 12

   Show what you knowExplain your thinking — What is 32.6 − 14.85?

   1. A17.75
   2. B18.75
   3. C17.85
   4. D17.25

   Explain your choice.
2. 13

   From Lesson 2.10Explain your thinking — Data set: 15, 18, 16, 17, 15, 72. Which measure of center best represents the data?

   1. AMedian, because 72 is an outlier
   2. BMean, because it uses all values
   3. CMean, because it is always best
   4. DNeither works for this data

   How do you know?
3. 14

   From Lesson 2.10Which measure better describes a 'typical' ticket?

   1. AThe median, because the $260 outlier pulls the mean far above most prices
   2. BThe mean, because it uses every value
   3. CNeither — you should use the mode
   4. DThe mean, because $85 is between the extremes

   How do you know?

Be honest — this tells your teacher what to do next