# Lesson: Front End Rounding: Sum with Decimals

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### Lesson Objective

SWBAT use front end rounding to estimate the sum of whole numbers and positive decimals to two places.

### Lesson Plan

Materials Needed: DN worksheet, dry erase markers, white board, blank paper, pencils
Vocabulary: rounding, estimation, actual, rounding off, decimals, place value

……….
Do Now (3 -5 min): Teacher gives each student a DN worksheet and asks them to complete the work as quickly and quietly as possible.

Opening (2 -3 min): Teacher quickly reviews answers to the Do Now and then says, “Yesterday we practiced rounding numbers and we just reviewed rounding with the DN worksheet. Today, we are going to learn a new skill. By the end of this lesson, you will be able to use rounding to estimate the sum of whole numbers and two positive decimals.”

Direct Instruction (10 min): Teacher begins “Ok! So lets say that you are in a store and you want to add the price of something in your head. Or you are talking to someone and they ask you to add or subtract a large number and you can’t just get out a calculator because you don’t always carry one around. What will you do? Well, you can use front-end rounding to estimate the total cost!”

Teacher continues, “Front end rounding is very easy as long as you use these two easy steps.” Teacher should write the following on the board:

1) Add the digits of the two highest place values
2) Insert zeros for the other place values

Teacher says, “Let me show you an example of how to use these steps. Lets say I have the number 4,657 and I want to add 3,491 to that number. I will round 4,657 to the nearest thousands place, which is 5,000 and then round 3,491 to the nearest thousand with is 3,000. Then I add, it is much easier to add 5,000 + 3,000. ” Teacher writes the following on the board:

4,647+3,491=
5,000+3,000= 8,000

Teacher says, “It is much easier to add numbers when you use front end rounding. Now, today we need to insert one more variable into the front end rounding equation. DECIMALS! However, this really doesn't change anything, because we will still be rounding to the largest place value in the number. Watch as I show you want I mean.” Teacher writes the following on the board and explains the thought process out loud as he/she writes:

\$44.96 + \$74.45=
\$45.00 + \$74.00= \$118.00

"When I am working with money and decimals, don't have to change much. In this problem, I rounded to the then nearest ones place. If I rounded to the nearest tens place my answer would have been different. Watch as I show you" [Teacher writes the following on the board]. "so I have to make sure I know which number I am rounding to and that I am paying attention to where my decimal is. My ones place is right before the decimal and when I round to it or anything higher both of my decimal places become zeros. Ok, let's try some together."

\$44.96 + \$74.45=
\$40.00 + \$70.00= \$110.00

Guided Practice (8-10 min): Teacher says, “Now, I will give you five problems to do together in groups of 2 or 3 on your own paper. Help each other as you work, because in a minute I will have you do some problems on your own. I want you to round all of these to the nearest ten before solving. Let’s get started.” Teacher writes the following on the board and gives each student time to solve the problems together in small groups.

\$53. 47 + \$98. 34 = _________ [\$150.00]
\$24. 67 + \$39. 78 = _________[\$60.00]
\$26.14 + \$55. 62 = ________ [\$90.00]
\$24.46 + \$69. 87 = ________ [\$90.00]
\$28.67 + \$44.28 = _________ [\$70.00]

Independent Practice (10 min): The teacher reviews the answers to the Guided Practice with the class and then has the students complete the following problems on their own using their own paper.

Round to the nearest ones place before solving.

\$78.34 + \$92.54 = _________ [\$171.00]
\$27.45 + \$59.23 = _________[\$86.00]
\$28.44 + \$13.23 = ________ [\$41.00]
\$68.66 + \$38.67 = ________ [\$108.00]
\$27.78 + \$91.13 = _________ [\$119.00]

Closing (2-3 min): Teacher calls the attention of the students back toward the front of the class to quickly review the answers to the Independent Practice/ ask what we learned about.

### Lesson Resources

 DN lesson 4 estimation   Starter / Do Now