# 4th Grade - Know When To Round Numbers

 Grade Level: 4th Skill: Numbers - large, small, prime and negative Topic: Know When to Round Numbers Goal: Decide when a rounded solution is called for and explain why such a solution may be appropriate. Skill Description: Decide when it is necessary to round in order to find a solution or if you need to find the exact solution by calculating.

## Building Blocks/Prerequisites

### Sample Problems

(1)

Decide if it is necessary to round.

Who Owns Hybrid Cars? (34)

 City Number of owners Los Angeles 44,212 Riverside 12,119 San Diego 24,208 San Francisco 16,912 Santa Barbara 5,219 Santa Maria 898

About how many more people own hybrid cars in Los Angeles than Santa Barbara?

How many people were surveyed in all? ____________ (103,568 people; exact number)

(2)

Enrollment in each class (34)

 Rooms Room 1 Room 2 Room 3 Room 4 Room 5 Enrollment 28 29 31 28 30

About how many children are in each class? ____________ (About 30 people)

Did you estimate or calculate? ____________ (Estimate, because I knew most of the numbers were close to 30, otherwise I would have to add, then divide. It was not necessary to determine the exact number, keyword “about”).

(3)

Estimate or Exact (48)

Do we need the exact or estimated number for the scenario below:

How many people called in to vote for the best dance group on I Know we can Dance?

(Exact number to determine how many votes each person received to decide the winner)

(4)

Rounding products(188)

If Joanne bought 8 packs of bagel at \$1.89 each pack. About how much money did she spend? ___________ (2.00 x 8 = \$16.00)

(5)

Rounding Decimals:

Every day May drives to work (5. 2 mi), to school (1.7 mi), to the gym (0.95 mi) and back home (6.8 mi.). About how many miles does May drive daily? _________ (about 15 miles, round the decimal to whole numbers).

### Learning Tips

 (1) Steps to rounding decimals-to the nearest whole number: Underline the digit to be rounded (ones place) Circle the digit to the right. If it is 0, 1, 2, 3, 4 the digit stays the same. If it is 5, 6, 7, 8, 9, the digit increases by one. The numbers to the right of the rounded digit become zeros. The steps are the same for rounding to the nearest tenth, just underline the digit in the tenths place. (2) Review Time: Analog clock- a clock that represents time by the position of hands on a dial Use an analog clock to practice telling time with your child. Thereafter, have him/her make estimates on how long it will take to do a task (i.e. looking at the amount of homework you have, how long will it take you to finish?) Do you need to give a specific time or can you round the time? Why? (3) Play games with money (http://www.moneyinstructor.com/play.asp - website has printable fake money) and estimate amount of money each player has. (4) How much will we spend? Use the sales papers from different stores and have your child shop for items. Have them estimate the costs and determine about how much will be spent at the store. Once your child has determined his/her estimated budget. Have them calculate the exact total and see if the amounts were close. (5) Categorize if you need to find the exact solution or if the solution can be rounded: Write some scenarios on an index card and your child will have to determine if he/she needs to know the exact amount or should he/she estimate the amount.

### Extra Help Problems

(1)

Animals in the zoo

 Type of animal Number of animals Giraffes 7 Flamingos 13 Monkeys 24 Birds 42 Lions 11

About how many birds and flamingos are at the zoo? _____ (40 + 10 = 50)

(2)

Round to find the sum:

3,379

+ 4,965

(3,000 + 5,000 = 8,000)

(3)

Round to find the sum:

947,501

+ 713,819

(900,000 + 700,000 = 1,600,000)

(4)

Round to find the sum:

836,127

+ 919,312

(800,000 + 900,000 = 1,700,000

(5)

Round to find the sum:

421,765

+ 391,090

(400,000 + 400,000 = 800,000)

(6)

Round to find the sum:

38,988

+ 2,566

(40,000 + 3,000 = 43,000)

(7)

The Number of Guests at Wemaway Camp Ground

 Month May June July August September Guests 346 865 1,291 1,765 521

What is the estimated difference of guests for June and August? ______ (2,000 – 900 = 1,100)

(8)

Estimate the difference:

864,341

- 713,190

(900,000 – 700,000 = 200,000)

(9)

Estimate the difference:

9,623

- 981

(10,000 – 1,000 = 9,000)

(10)

Estimate the difference:

3,610

- 1,849

(4,000 – 2,000 = 2,000)

(11)

Estimate the difference:

135,231

- 91,210

(100,000 – 90,000 = 10,000)

(12)

A whale ate 392 lbs of fish on Saturday and 212 lbs of fish on Sunday. About how many pounds of fish did he eat over the weekend? (400 + 200 = 600 lbs)

(13)

Jesse bought 5 pairs of jeans at \$19.98; 8 shirts that cost \$ 7.79; 2 packs of socks for \$5.49; and I pair of shoes for \$46.10. About how much did Jesse spend at the mall? ______________

(5 x 20 + 8 x 8 + 2 x 5 + 46 = \$220.00)

(14)

Round the factors to find the product:

287 x 6 = _____

(300 x 6 = 1,800)

(15)

Round the factors to find the product:

\$19.95 x 7 = _____

(20 x 7 = \$140.00)

(16)

Round the factors to find the product:

389 x 47 = ______

(400 x 50 = 20,000)

(17)

Round the factors to find the product:

\$812.18 x 5

(800 x 5 = 4,000)

(18)

Round the factors to find the product:

999 x 3 = _____

(1,000 x 3 = 3,000)

(19)

After eating at their favorite restaurant, five friends decided to split the bill evenly. The cost of the meals were:

\$8.69

\$9.99

\$3.47

\$11.29

\$12.19

5 drinks for \$1.25

Tax: \$4.28

Tip \$10.00

How much did each person have to pay?

Do we need to round or calculate the exact number? Why?

(The exact number needs to be calculated in order to pay the bill accurately. Each person paid \$13.23)

(20)

Round decimals:

16.29 + 4.74

(16 + 5 = 21)

(21)

Round decimals:

12.19 – 4.92

(12 – 5 = 7)

(22)

Decide if you need the exact solution or can you round:

How many people did you see at the carnival?

(round)

(23)

Decide if you need the exact solution or can you round:

How much does it cost for school lunch?

(exact)

(24)

Decide if you need the exact solution or can you round:

How much money do you need to shop for school clothes?

(round)

(25)

Decide if you need the exact solution or can you round:

The cost of bus fare.

(exact)