Start here

Use the model to solve the first problem. Then try these quick review questions from earlier lessons.

1. 1

   Same stepsFinish what the group started. Use the model above, step for step. 🔊 Listen 💡 Hint

   Try it together — then prove it:

   1. Add 12.45 and 7.8.
   2. Write 7.8 with two decimal places. Line up the points. (7.80)
   3. Add from right to left. What is the sum? (12.45 + 7.80 = 20.25)
   4. Why do we line up the decimal points, not the last digits? (Lining up the points puts tenths with tenths and hundredths with hundredths. Each column then holds one place value.)

   Show your work
2. 2

   Quick reviewA data set has one very large outlier. Which measure of centre does it pull on MORE? 🔊 Listen 💡 Hint

   1. AThe median
   2. BNeither one
   3. CThe mean
   4. DBoth equally

   How do you know?
3. 3

   Quick reviewHouse prices on a street are $180,000, $190,000, $200,000, $210,000 and $2,000,000. Which measure best describes a typical price? 🔊 Listen 💡 Hint

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

   How do you know?
4. 4

   Quick reviewA data set is roughly symmetric with no outliers. Which measure of centre is a good choice? 🔊 Listen 💡 Hint

   1. AThe range
   2. BOnly the maximum
   3. CThe mean
   4. DNeither the mean nor the median

   How do you know?

Try these on your own

Choose an answer. Then explain how you know.

1. 5

   Think it through2.45 + 2.60 + 2.38 = ? 🔊 Listen 💡 Hint

   1. A6.43
   2. B7.143
   3. C7.43
   4. D7.53

   Why is that the answer?
2. 6

   Think it throughWhy is it safe to rewrite 2.6 as 2.60? 🔊 Listen 💡 Hint

   1. AIt makes the number ten times bigger
   2. BAdding a zero at the end of a decimal does not change its value
   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? 🔊 Listen 💡 Hint

   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

   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? 🔊 Listen 💡 Hint

Use the words

Fill each blank with a word from the bank.

• 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.
• The second place to the right of the decimal point is the ___ place.

Explain the thinking

1. 9

   Find the mistakeRead the mistake. Explain what went wrong, then show the correct step. 🔊 Listen 💡 Hint

   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? 🔊 Listen 💡 Hint
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. 🔊 Listen 💡 Hint

   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? 🔊 Listen 💡 Hint

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

   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? 🔊 Listen 💡 Hint

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

   How do you know?
3. 14

   From Lesson 2.10Which measure better describes a 'typical' ticket? 🔊 Listen 💡 Hint

   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?

Check your progress

Choose the box that best describes how you feel about each skill.