Return to Mathematics IndexMeasuring Mixed Numbers

Karen Trout Sumner Math and Science Academy

4320 W. 5th Avenue

Chicago IL 60624

(312) 534-6730Objectives:

Grade 5

-Students will discover the need and every day use of mixed numbers.

-Students will measure different lengths to the nearest fraction of an

inch.

-Students will review the equivalent values of fractions (for example:

2/4=1/2).

-Students will review how to come up with the common denominator and why.

-Students will add mixed numbers phenominologically and then

algorithmically.Materials Needed:

-1 pair of scissors per student

-1 ruler per student

-5 pieces of tape per student

-1 worksheet per student

-1 piece of scratch paper per student

-Construction paper of different colors

-Large clear container with graduated cups

-Measuring cup set

-Bucket full of milky water (mix in a little corn starch)Strategy:

1. Before class, use your construction paper to make a couple sets of

fraction bar charts (be sure to include whole, halves, fourths, eighths, and

sixteenths). Use different colors for each different fraction length, and make

your pieces board size.

2. If you have a large container that does not have graduated cups, just

place a strip of tape down one side of the container, then pour a cup of water

in at a time and mark the level for each cup on the piece of tape.

3. Create a worksheet that has about 4 different problems similar to the

example below. Draw different length bars that the students will have to

measure individually, cut out, connect, and then remeasure as a whole unit.

They will only be measuring the length of these rectangles or bars which should

be at various lengths between 1/2 an inch and 5 inches. This is a sketchy

example of what one problem would look like:

Measure these lengths as accurately as you can, then cut them out, tape

them together and remeasure the length of these two together:

`ffffffffffffffffffffffffp `fffffffffffffffp

w w w w

w w + w w =

w w w w

affffffffffffffffffffffffq afffffffffffffffq

4. Begin the class with this question: "Pretend you are a zookeeper and

your responsibility is to feed the baby animals their formula each day. The

baby porcupine eats 2 1/2 cups of formula, the baby seal eats 5 1/4 cups, and

the baby ape eats 7 3/4 cups. How much baby formula do you need to make to feed

all three of the baby animals?"

5. Allow the class time to reflect on the problem and then explain that

they are going to need to understand how to add mixed numbers in order to solve

this problem. Demonstrate for them briefly on the board how they are going to

use the worksheet. They are to measure the length of each bar and write that

length inside the figure. Then they are to cut out each bar and connect

them with tape onto the piece of scratch paper they have been given. They

should now have a longer bar which they are to measure and write down the total

length of the two bars combined.

6. When they have completed this worksheet go back and compare some of

their answers. Then using the fraction pieces which you will have taped up on

the board, show them the different lengths. If they measured 3 1/2 inches for

one bar, show them 3 1/2 in fraction pieces. If their second bar was 1 1/4

inches long, then show them 1 1/4 in fractions. Demonstrate for them how to add

those two fractions of different denominators (1/4 and 1/2) by replacing the 1/2

fraction piece with two 1/4 pieces and finding their length to remain the same.

Using the fraction pieces, continue to visualize for them how we come up with a

common denominator when adding fractions of unlike denominators.

7. When you feel they have grasped this concept, you then go back to your

original question about feeding the baby animals. This time have them find the

common denominator between 1/2 and 1/4 and then add their mixed numbers together

to get the total amount of baby formula needed.

8. Finally, to prove whether or not the answer they got on the baby

formula was correct, have someone come up and measure out the amount of cups fed

each baby animal. Have them take the milky water (water and a little corn

starch) out of the bucket and carefully pour it into your graduated, clear

container. The amount of formula that is now in the container should be the

same as the amount of cups the class came up with on paper.Conclusion:

The students visualize adding mixed numbers physically by adding different

lengths together to the nearest fraction of an inch and by adding cups together.

Then they discover the simplified algorithmic process which reduces the amount

of work they need to do. However now they also understand why they need to add

mixed numbers and what mixed numbers are. In conclusion, their performance

should improve greatly as they comprehend the usefulness of these skills and

what it is that they are actually doing when they come up with a common

denominator and add their mixed numbers together.