Estimation
is when one judges the approximate value, size or worth of something.
If we are estimating values, there are generally two approaches
that are used:
1.
Rounding: A rounded number has about the same value as
the number you start with, but it is less exact.
Here
is the general rule for rounding:
-
If
the number you are rounding is followed by 5, 6, 7, 8 or
9, round the number up. Example: 38 rounded to the nearest
10 is 40.
-
If the number you are rounding is followed by 0, 1, 2, 3
or 4, round the number down. Example: 33 rounded to the
nearest 10 is 30.
2. Truncating or Front End Rounding — Truncate
means to shorten or cut off. A number that is truncated has all
the numbers changed to 0 after the number you are rounding. For
example, if you are truncating to the tens place, 57 = 50 and
429 = 420.
The
grocery store is a great example of a place where math is real
and estimation skills are important. Did you ever have $10 and
need a few things at the store? How do you know when you’ve
bought everything you can afford? How do you figure the tip in
a restaurant? By using estimation, of course.
Some
things you might do to improve estimation skills include:
-
Have
students estimate how much milk they drink in a week and figure
out how many gallons they would have to buy.
-
Have a variety of items and a scale available. Have students
estimate the weight of the items and then weigh them to find
the actual weight. This can then be graphed into a scatter
plot.
-
Have the students examine a variety of items that have the
price tags hidden. Let them estimate the actual cost.
-
Using
catalogs, have each student cut out product pictures and glue
them to a piece of paper. They can keep a list of each product’s
price on a separate piece of paper. Then have them exchange
papers and estimate the costs of the items on the list. They
could then compare this to the actual costs.
-
Bring in a shopping bag full of groceries. Let the students
lift it and estimate the weight of the bag.
Estimating
time is not as easily accomplished. Tell the students to put their
heads down and lift them when they think one minute is over. Write
the exact time that they started on the board. They can then write
down the time they estimated as being one minute.
Web
Resources
Estimation
http://www.aaamath.com/est.html
Estimation
Contraption Game
http://pbskids.org/cyberchase/games/
ballparkestimation
Estimation — What Do You Think? http://www.forsythcountyschools.net/kadkins/
estimate.htm
Rounding
Numbers
http://www.oswego.org/testprep/math4/
d/roundingl.cfm
Spending
Spree for Primary Grades
http://www.primarygames.com/Spending%20Spree/
start.htm
Time
Estimation
http://www.explorelearning.com/index.cfm?method=
cResource.dspDetail&ResourceID=50
