2.3.4 Rounding in the Real World

Activity symbol Activity: How Much is It?

Suppose you want to buy a new truck. When you visit the dealership’s website, it says the cost of the vehicle you are looking at is $29,748. When you call the dealership on Thursday, the sales representative, Joe, tells you the cost is $29,750 and the next day another sales representative, Tina, informs you that the car costs $29,700. Why did the quote you were given on the cost of the truck change?

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Discussion

Round the website cost to the closest $10. Then round the website cost to the closest $100.

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Answer

Here’s how the variation in the quotes happened:

Rounding to the closest $10 (this is the same as rounding to the tens): The digit 4 is in the tens place. Looking to the next smaller place value (to the right), the digit is an 8. Since 8 is larger than 5, we round up the 4 to 5 in the tens place. Finally, we replace the units digit with 0 (because this place is to the left of the decimal point). The rounded number is $29,750. This explains Joe’s quote.

Rounding to the closest $100 (this is the same as rounding to the hundreds): The digit 7 is in the hundreds place. Looking to the tens place (to the right of the 7), the digit is a 4. Since 4 is less than 5, we leave the digit 7 unchanged and replace the digits after the 7 with zeros. The rounded number is $29,700. This explains Tina’s quote (which is more appealing than Joe’s since it’s less).

Want to be a mathionaire? Check out this rounding game [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] for a little extra practice!

Notepad symbol Activity:  Thinking About Your Learning

It is a good time now you are nearly at the end of the Unit 2 to think about how your learning has gone so far.  Maybe you think that you need to change some aspects of how you are studying—is your math notebook organised in a way that is helping you?  Have you found the best time to study for you?  Do you think that you might need to take more notes?

Jot down some thoughts now in your math notebook that you can look back on when you start Unit 3.  

So far, we’ve studied how to write and estimate numbers. Now we will begin to perform calculations with them. First, let’s look at addition and subtraction of numbers.

2.3.3 More Practice Rounding

2.4 Self-Check on Unit 2