Why Do We Round Numbers?

While walking in the Wonderopolis pasture, we overheard a conversation between two wolves:

Wolf 1: Hey Wayne! What are you doing with those binoculars?

Wolf 2: Howdy Wendell! I’m counting the sheep in the pasture. 176…177…178…

Wolf 1: Cool! That would make me sleepy. Why are you counting them, though?

Wolf 2: I invited all of them to a birthday party and I need to know how many pieces of cake I’ll need. 181…182…183…

Wolf 1: Really? Whose birthday party is it?

Wolf 2: It’s my party! 186…187…188…

Wolf 1: But…how did you get sheep to come to a wolf’s party?

Wolf 2: I wore my wool sweater when I invited them! 191…192! I’ll round up to 200 so I’ll be sure to have enough cake.

Suspecting something was amiss, we went to find the shepherd to inform him about the wolf’s party invitation. However, the conversation between the wolves made us ponder about the concept of rounding numbers. Why do we do it exactly?

If you’ve taken math classes for a long time, you have probably learned the process of rounding numbers. The most common method involves selecting the last digit to keep (the digit being rounded to). Then, examine the next digit: if it is less than five, keep the last digit the same (round down). If it is five or more, increase the last digit by one (round up). Lastly, replace the digits after the last digit with zero (or omit them entirely if rounding a decimal).

Let’s revisit Wendell the Wolf’s example to clarify. He counted 192 sheep and decided to round to the nearest hundred. The hundreds place had a 1, which is the last digit to keep. The next digit was 9, which is greater than 5. So Wendell rounded up by adding 1 to the 1 and replacing the other digits with zeros, resulting in 200.

What if Wendell had chosen to round to the nearest ten? He counted 192 sheep, so the tens place had a 9, which is the last digit to keep. The next digit was 2, which is less than 5. Therefore, Wendell would have rounded down by keeping the last digit the same and replacing the remaining digit with 0, resulting in 190.

Rounding numbers simplifies them and makes them easier to work with. Although they may be slightly less accurate, their values remain relatively close to the original numbers. People round numbers in various situations, including real-life scenarios that occur regularly.

For instance, when calculating the sales tax for a planned purchase, the result may be something like $1.7894. Since change is handled in hundredths, rounding up to $1.79 is necessary.

Similarly, when performing mental calculations to determine the number of candy bags you can buy at a store, rounding numbers provides a convenient method. If you have $7 and the candy bags cost $1.79, you know you can purchase 3 bags of candy.

Do you know how to determine the price of a bag of candy without doing exact calculations? One way is to round the price up to $2, which takes sales tax into consideration and gives you an estimate on the high side. By doing this, you can quickly figure out that 3 bags of candy would cost about $6 and 4 bags would cost about $8.

Working with rounded numbers is often easier because exact numbers are not always necessary. For example, if it takes approximately 25 minutes to get somewhere, it’s simpler to allow yourself 30 minutes of travel time. Similarly, when talking about the population of New York City, it’s easier to work with a rounded figure of 8 million people rather than the exact figure of 8,214,426 people.

Give It a Try

Are you ready to practice addition, subtraction, multiplication, and division? Don’t forget to try out the following activities with a friend or family member:

  • If you’re curious to learn more about rounding numbers, you can watch Math Playground’s How To Round Whole Numbers video online. Once you understand the process, try explaining it to someone else.
  • Think you’re a rounding pro? Put your skills to the test by playing the fun Rounding Game online. Challenge your friends and family members to see who can achieve the highest score.
  • If you want to practice rounding numbers in real-life situations, ask an adult friend or family member to take you on a trip to a local grocery store. With a budget of $20, round the prices of items up to the nearest whole dollar and determine how many items you can purchase. Check to see how accurate your estimates were at the checkout counter!

Additional Resources

  • http://www.mathworksheetscenter.com/mathtips/roundingnumbers.html
  • http://www.bbc.co.uk/skillswise/factsheet/ma06roun-e3-f-more-practical-examples-of-why-we-round-numbers
  • https://www.mathsisfun.com/rounding-numbers.html

Leave a Reply

Your email address will not be published. Required fields are marked *