Using Rounding to Estimate

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SWBAT use rounding to estimate solutions to multiplication problems.

Big Idea

Rounding is one way to estimate products.


5 minutes

In the Introductory Video for Using Rounding to Estimate, I introduce the lesson for today.

 To relate this lesson to their every day lives, I ask the students a question.  "Is there ever a time that you may need to estimate?"  I call on a few students to share their ideas about when they would need to estimate.  By providing this informaiton, the students can see how this lesson is important in their lives.

"Today, you learn to estimate greater numbers.  In previous lessons we have estimated smaller numbers, but you need to know how to estimate greater numbers.  What are some things that you may need to estimate that is a large number?"  Take a few responses from the students.  


Direct Instruction

10 minutes

I like for my students to come to the carpet when I am teaching from my Smart board.  This allows every student the ability to hear and see what is being said and done on the Smart board.  The  Using rounding to estimate power point is already displayed on the board.

I start the lesson by review the rules of rounding.  I tell the students to underline the place to be rounded.  If the place behind the underlined digit is 5 or more, the underlined digit goes up by 1 and everything behind it become zeros.  If the place behind the underlined digit is 4 or less, the underlined digit stays the same and everything behind it become zeros.

I present the students with the following problem:  

Our school has 425 students.  Each student will receive 3 pencils.  About how many pencils will be given out to the students in all?  To find out approximately how many pencils are being given out, we can round.
425 x 3=

Round 425 to the nearest hundreds.  There is a 2 behind the 4.  Use the rule for 4 or less to round the 4.  The 4 will stay the same, therefore, 425 is approximately 400.  

 400 x 3 = 1,200

Remember to use what we have learned about multiplying by multiples of 10 and 100. (MP7 Make use of structure)

400 is a multiple of 100, so you multiply the factors, then add 2 zeros.
Now, you will practice this skill in groups.

Group or Partner Activity

20 minutes

To give the students the chance to practice with their classmates, put the students into groups of 3.  Small groups tend to work better in my classroom because I can make sure all students are lending their voice to the conversation.  Each student will have a role in this activity.  There will be player 1, player 2, and scorer.  Each group will receive an activity sheet and a number cube to use for this activity. 

Activity:  Who's First?

The students will play a game for this activity.  In previous lessons the students have used rounding so they should understand the concept.  However, in this lesson, the students will be rounding greater numbers and then multiplying them.  

The rules of the game are as follows:

1.  Two students will be competing with each other to multiply a problem.

2.  The first person to get it correct wins.

3.  Player 1 will role a number cube 4 times.  The first number will be the first factor.   The last 3 numbers will be used as the 3-digit multiplier.  Round the last 3 numbers to the hundreds place.

4.  The third person in the group will monitor the time and keep score.  The students will have 1 minute to solve the problem.  If no one solves the problem, then no one gets a point.  The person who solves it first, gets the point.

5.  The students will switch roles (clockwise).  The person monitoring the time will now become a player.


Independent Activity

10 minutes

I always give my students an independent assignment because I want to know what each individual student knows.  In groups, some students hide behind the knowledge of other students.  With the independent assignment, I know exactly who knows what.

For this Independent Assignment Using Rounding to Estimate, the students use rounding to estimate a product.  They need a piece of paper and pencil to complete this assignment.



Tina has 3 boxes in her closet.  There are 194 books in each box.   About how many books does she have in all?



10 minutes

To close the lesson, I bring the class back together as a whole to discuss the independent assignment.  I call on a volunteer to answer the question.  I use this as a teaching opportunity for those students who still have not mastered the lesson.

I like to end my lesson with students summarizing what they have learned for the day.  This gives me another assessing opportunity to see what my class really knows.

Possible student summary:

I learned to underline the place that I want to round.  Next, I look behind the underlined number.  If the number is a 5 or more, I round up by 1 and everything else become zeros.  If the number is 4 or less, my number stays the same and everything else become zeros.