# Lesson: Front End Rounding: Difference with Decimals

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### Lesson Objective

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

### Lesson Plan

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

……….
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 learned how to use front end rounding to estimate a sum with decimals. Today, we are going to use front end rounding to estimate a difference with two decimals. By the end of this lesson, you will be able to use front end rounding to estimate the difference of whole numbers and two positive decimals.”

Direct Instruction (10 min): Teacher begins “Ok! Think back to yesterday. I gave you an example of going into the store. Now you’re in the store and things are on sale. You want to figure out how much money you’re saving so you can get yourself something with the savings. You don’t have a calculator, so you need to rely on you skills! What do you do? Well, you use front-end rounding to estimate the difference!”

Teacher continues, “Let’s review the two steps to  front end rounding.” 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. ” Teacher writes the following on the board:

\$46.47- \$34.91=
\$46.00 – 35.00 = \$11.00

Teacher says, “It is much easier to subtract numbers when you use front end rounding. Watch as I do one more before we work on some together.” Teacher writes the following on the board and explains the thought process out loud as he/she writes:

\$82.96 + \$51.45=
\$83.00 + \$51.00= \$32.00

"When I am working with money and decimals and subtraction I have to pay attention. In this problem, I rounded to the then nearest ones place.  I didn’t have to regroup, but since I am subtracting I need to pay attention for that. Regrouping means that I would have to reorganize my numbers so that a larger number is on top, making it possible to subtract. What as I change this problem slightly and see the additional work I have to do.[Teacher writes the following on the board]. "So now there is a 3 and a 9 in the ones place. I know I can’t take 9 things away from 3 things, so I have to regroup. Making my 8 in the tens column a 7 and the 3 now a 13. Only now can I subtract to find my answer.Ok, let's try some together."

\$82.96 + \$59.45=
\$83.00 + \$59.00= \$24.00

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.

\$88. 34 - \$34. 47 = _________ [\$60.00]
\$39. 78 - \$24. 67 = _________[\$20.00]
\$55. 62 - \$26.14 = ________ [\$40.00]
\$79. 87 - \$54.46  = ________ [\$30.00]
\$44.28 - \$28.67  = _________ [\$10.00]

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. Pay attention you will need to regroup for some of these.

\$92.54 - \$78.34 + = _________ [\$14.00]
\$59.23 - \$27.45 = _________[\$32.00]
\$98.44 - \$13.23 = ________ [\$85.00]
\$63.66 - \$38.67 = ________ [\$25.00]
\$91.13 - \$77.78 - = _________ [\$13.00]

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 5 estimation   Starter / Do Now
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