Addition was used for combining numbers together. In what type of situation would you use subtraction?

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• Comparing numbers (how much larger, how much smaller)
• How far apart
• Removing from a total or from a group

What hints might you see in a word problem to indicate that you would use subtraction?

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• Situations where you are taking a piece away from a whole group
• Comparing how much larger or smaller one thing is than another
• Finding the distance between two objects

Read the following word problem and answer the questions below using your notes. If you need a hint, you can hover your cursor over the word 'hint.'

The words "how much less" were a clue that you should use subtraction in this problem. Brainstorm a list of other words that could be used in a word problem to indicate using subtraction. Record the list in your notes.

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Difference, less, decrease, loss, subtracted from, how much less, how much more, how much larger, how much smaller, decrease, reduce, take away, minus.

You and your lab partner are taking temperature measurements during a science lab. You put a thermometer in a beaker of hot water and record the temperature every minute as it cools. Part of the data chart is shown below:

 Time (minutes) Temperature (°C) 0 75 1 73 2 70 3 68 4 65 5 62

What is the difference in temperature between the first reading (at time = 0 minutes) and the last reading (at time = 5 minutes)?

Which mathematical operation should you use to solve this problem?

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Subtraction

How did you know which operation to use?

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The problem used the phrase, "What is the difference in temperature" that means we are finding how much larger or smaller one number is than another.

Which two numbers should you use from the table?

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75°C and 62°C.

Why did you select those numbers?

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They are the temperatures that go with the times given in the problem.

Write an equation that you could use to solve for the difference in temperature, T.

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T = 75 – 62

What was the difference in temperature?

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T = 13. The difference in temperature is 13°C.