ESTIMATION

•  Estimation can be a powerful tool in mathematics. You can use it to check an answer when you are finished solving a problem, and it will tell you whether or not your answer is reasonable. If your answer is somewhat close to your estimate, you know that you are on the right track. If your answer is off by hundreds, thousands, or more, you know that you need to revisit the problem and check over your work. Sometimes you may have missed something simple, like not lining up place value columns, or putting a decimal point in the wrong place. Sometimes you have to go back to the beginning and start again. Your estimate tells you when that is necessary, rather than waiting until you suffer the consequences of a wrong answer, like a bad grade on a test or paying too much for materials at the hardware store.

• An estimate is also useful for finding an answer quickly when an approximate answer is good enough. If you are the host of a buffet dinner and want to know about how many people are coming so you can put out enough potato salad, and estimate will probably work. However, if it is a sit - down dinner where every guest has a steak or filet on his or her own plate, an estimate is not very practical. It may leave you with too many, or even worse, too few plates to set before your guests. Knowing when to use an estimate, and when to solve for an exact answer is a life skill that comes with practice.

• Shopping is an excellent activity to help you practice your skills of estimation. If you have twenty-three dollars, and you are buying something that costs $9.98, you can quickly change the numbers to friendly numbers in your head by rounding. Twenty-three is close to 20, and $9.98 is close to 10.  If you have $20 and spend $10, you will have $10 left. As you go into the music store, you keep in mind that you have about ten dollars to spend.  This saves you time as you look for a CD to play during your party. You know that if the CD costs more than ten dollars, you will not have enough money to buy it, so you look in the section marked $8.99 and under.  When you find a CD you think you want, you can look on the back and estimate again. If the playing time says 129 minutes, you can estimate that it plays for about two hours, since that would be 120 minutes. Yes, estimation can be a very useful tool.

 Name:__________________________________

Answer the following questions based on the reading passage. Don’t forget to go back to the passage whenever necessary to find or confirm   your answers.

1)  What is one beneficial thing about using estimation?

2)  What is the difference between an approximate answer and an exact answer

3)  What is meant by the term friendly number?

4)  Describe a time when you used estimation. How was it helpful?

5) Use what you have learned. What is a good estimate for 48 + 37? Round to friendly numbers, and then estimate the sum.