# Rounding 3-Digit Numbers to the Nearest Ten, plus EstimationA free lesson for 3rd grade math

Rounding to the nearest ten

This number line has the whole tens marked (720, 730, and so on). Let's think about all of the numbers between 740 and 750. Which of them are nearer to 740 than to 750?
Which ones are nearer to 750? Rounding a number to the nearest ten means finding which whole ten the number is closest to. We use the symbol ≈ when rounding. Read it as “is approximately” or “is about”.

Read the examples below. They are also illustrated on the number line with arrows.

 731 ≈ 730 (731 is approximately 730) 767 ≈ 770 (767 is about 770) 724 ≈ 720 (724 is approximately 720)
Numbers that end in 1, 2, 3, or 4 are rounded down to the previous whole ten.
Numbers that end in 5, 6, 7, 8, and 9 are rounded up to the next whole ten.
Notice that numbers ending in 5 are rounded up even though actually they are as far from the previous whole ten as they are from the next whole ten. For example, 855 is equally far away from 850 as it is from 860, but 855 ≈ 860 when rounding to the nearest ten.

1. Round the numbers to the nearest whole ten. Use the number line to help.

 a.  243 ≈ _______ b.  287 ≈ _______ c.  251 ≈ _______ d.  298 ≈ _______ e.  266 ≈ _______ f.  214 ≈ _______ g.  255 ≈ _______ h.  295 ≈ _______ i.  307 ≈ _______ j.  302 ≈ _______ k.  276 ≈ _______ l.  242 ≈ _______ Whole hundreds are whole tens, too Remember that 100, 200, 300 and all of the other whole hundreds are also whole tens. Why? Remember 100 is 10 tens. 200 would be 20 tens. So, when rounding 603 to the nearest whole ten, we get 603 ≈ 600. And 799 ≈ 800.

2. Round the numbers to the nearest ten.

 a.  402 ≈ _______     897 ≈ _______ b.  396 ≈ _______     393 ≈ _______ c.  804 ≈ _______    805 ≈ _______ d.   97 ≈ _______    997 ≈ _______

 Estimation When we use rounded numbers to calculate with, that is called estimation. Mrs. Spencer, the principal, bought books and notebooks for \$547, pencils for \$38, and erasers for \$31. We can estimate her total bill by rounding these numbers to the nearest ten, and adding: \$550 + \$40 + \$30 = \$620. Her total bill is about \$620.

3. Estimate the total bill.

 a.  a computer, \$296, and desk, \$188 computer about \$___________ desk about \$___________ total bill about \$ ___________ b.  a tennis racket, \$123, and balls, \$38 racket about \$___________ balls about \$___________ total bill about \$ ___________ c.  a movie, \$29, MP3 player,  \$99, and pants, \$32           total bill about \$ ___________ d.  a printer, \$65, paper \$13, and printer ink \$117        total bill about \$ ___________

4. Write the previous and the next whole ten, then round the number.

 a.  ______, 472, ______ 472 ≈ _________ b.  ______, 829, ______829 ≈ _________ c.  ______, 514, ______514 ≈ _________ d.  ______, 317, ______ 317 ≈ _________ e.  ______, 608, ______608 ≈ _________ f.  ______, 455, ______455 ≈ _________

5. Anna wants to buy a bicycle for \$129. Round this number to the nearest ten.
She earns \$30 each week. How much does she earn in two weeks?

In three weeks?

In how many weeks does she have enough to buy the bicycle? 6. Estimate, using rounded numbers, the total distance
all the way around this triangular path in the forest.
Also find the real distance by adding the original
numbers in columns. Estimate: ___________________ ft

7. Round each number to the nearest
whole ten. Place each answer in the
cross-number puzzle.

 a. c. b. c. d. e. e.
Across:

a. 633

b. 796

c. 447

d. 54

e. 306

Down:

a.  655

b. 819

c.  397

d.  512

e.  911

This lesson is taken from Maria Miller's book Math Mammoth Add & Subtract 3, and posted at www.HomeschoolMath.net with permission from the author. Copyright © Maria Miller..

#### Math Mammoth Add & Subtract 3

A self-teaching worktext for 2nd-3rd grade that covers mental addition & subtraction with three-digit numbers, regrouping with three-digit numbers (carrying and borrowing), rounding, estimating, and word problems.