Rounding, Estimating and Justifying

1
Rounding, Estimating and Justifying
By
4.5(A) round whole numbers to the nearest ten,
hundred, or thousand to approximate reasonable
results in problem situations 4.5(B) estimate a
product or quotient beyond basic facts. Use
strategies including rounding and compatible
numbers to estimate solutions to multiplication
and division problems. 4.14(D) use tools such as
real objects, manipulatives, and technology to
solve problems.
2
Rounding to the nearest 1000

• What would these numbers be if they were rounded
  to the nearest 1000?

25,998
2345
989
10,303
77,099
45,913
3
Rounding to the nearest 100

• What would these numbers be if they were rounded
  to the nearest 100?

245
989
303
880
499
913
4
Rounding to the nearest 10

• What would these numbers be if they were rounded
  to the nearest 10?

99
80
45
38
92
56
70
22
45
5
Solve this problem and justify your answer.

• Marias teacher gave her five numbers 6, 7, 3,
  8, and 5. The teacher told her to make the
  largest number possible using all these numbers
  and placing the 7 in the tens place. What is the
  largest number Maria could have made?

6
7
3
8
5
6
Solve this problem and justify your answer.

• Jesse has 6 horses. 2 Arabians weight
  approximately 420 kilograms each. 2 Thoroughbreds
  weigh approximately 490 kilograms each. 2
  Palominos weight approximately 580 kilograms
  each. Which is the best estimate of how much less
  the combined weight of the palominos is than the
  combined weight of the Arabians and the
  Thoroughbreds? Remember to round your numbers.

600 kg, 1,500 kg, 800 kg, or 200 kg?
7
Solve this problem and justify your answer.

• Lenny has 9 nails to use in a science experiment.
  The shortest nail is 29 millimeters long, and the
  longest nail is 51 millimeters long. Which is the
  most reasonable estimate of the total length of
  all 9 nails?

Less than 50 mL, between 50 and 250 mL, between
250 and 450 mL, or more than 45mL?
8
Solve this problem and justify your answer.

• Joseph has 2 containers. One container has 8,789
  milliliters of water in it. The other container
  has 7,005 milliliters of water in it. Joseph
  pours all of the water from these 2 containers
  into a large bucket. He then pours 1,892
  milliliters of water from the bucket into a jar.
  Approximately how many milliliters of water are
  still in the bucket?

Fewer than 11,000 mL, between 11,000 and 12,000
mL, between 12,000 and 13,000 mL, or more then
13,000 mL?
9
Solve this problem and justify your answer.

• Snook Elementary students are going to a museum.
  Each ticket to the museum costs 5. There are 31
  groups of students, and each group is made up of
  19 students. Which is the most reasonable
  estimate of the total cost of the tickets?

Less than 2,900, between 2,900 and 3,100,
between 2,100 and 3,300, or more than 3,300?
10
Solve this problem and justify your answer.

• The city is expecting a large crowd for a live
  rock concert. City officials are concerned about
  the number of available public parking spaces.
  There are 2,985 parking spaces in lot A. However,
  812 of these spaces will be blocked off for band
  members, workers, and special guests. City
  officials have decided to open another 1,295
  spaces in lot B for public parking. About how
  many spaces are available now for public parking?
  

• 900 spaces, 2,500 spaces, 5,100 spaces or 3,500
  spaces?

11
Solve this problem and justify your answer.

• Each person in the United States produces an
  average of 1,609 pounds of garbage a year. Each
  person in Australia produces an average of 1,521
  pounds of garbage a year. Each person in Canada
  produces an average of 1,455 pounds of garbage a
  year. Which is a reasonable estimate of the total
  amount of garbage produced yearly by a person in
  the United States and a person in Canada?

• 1,000 lbs, 2000 lbs, 3,000 lbs, or 4,000 lbs?

12
Solve this problem and justify your answer.

• Jose plays quarterback for his elementary team.
  He averages 23 throws a game. Which is the best
  estimate of the number of throws Jose makes in a
  season (12 games)?

• Less than 100, between 100 and 300, between 300
  and 600 more than 600?

13
Solve this problem and justify your answer.

• In 1998 there were 5,813 registered voters in
  Refugio County and 718 registered voters in
  McMullen County. However, only a total of 2,724
  of these registered voters voted in the election.
  What is the best estimate of the difference
  between the number of people registered to vote
  in these counties and those who actually voted in
  the election?

6,000 people, 2,200 people, 3,800 people or 9,200
people?
14
Solve this problem and justify your answer.

• Alex and Garrison had a contest to see who could
  sell the most popcorn for their scout group. Alex
  sold 4 cases of 48 boxes of popcorn that cost 10
  each. He also sold 8 cans of caramel corn for 15
  each. Garrison sold 5 cases of 48 boxes of
  popcorn, as well as 10 cans of caramel corn. What
  is the best estimate of the number of boxes of
  popcorn that both Alex and Garrison sold?

• 100 boxes, 125 boxes, 360 boxes, or 450 boxes?

15
Your turn. Choose one of these answers and design
a problem to find that answer.

• Less than 1,300
• Between 1,300 and 1,500
• Between 1,500 and 1,700
• More than 1,700

16
Your Turn again!
17
ANSWERS

• Slide 5 86,573
• Slide 6 200 kg
• Slide 7 Between 250 and 450 millimeters
• Slide 8 Between 12,000 and 13,000 milliliters
• Slide 9 Between 2,900 and 3,100
• Slide 10 3,500 spaces
• Slide 11 3,000 pounds of garbage
• Slide 12 between 100 and 300
• Slide 13 2,200 people
• Slide 14 450 boxes

18
Practice with Rounding

• Rounding Concentration Game
• Mystery Picture Place Value
• Place Value Puzzler
• Place Value Program
• Rounding Flashcards
• Hangman Rounding (Challenging!)

19
Lesson Plans

• You can use this with your multimedia machine/TV
  as a class lesson or problem of the day.
• You can use this in centers with your students to
  reinforce rounding, estimating, and place value
  skills (dont forget to take out the answer
  slide, number 17, and this slide)
• You can use this as practice or an assessment in
  the computer lab with a whole class. (Be sure to
  take out the answer slide, number 17 and this
  slide)
• Have students place their work, pictures,
  numbers, and words on any blank space on the
  slide.