Return to Mathematics IndexAdding Mixed Numbers with Unlike Denominators

Camille Gales Edward Coles Elementary School

8441 S. Yates Blvd.

Chicago IL 60617

(773) 535-6550Objective:

This is a seventh grade activity designed to provide students with practice in

adding mixed fractions with unlike denominators.Materials:

tape measures; water soluble marking pens; 12 inch rulers; teacher made block

letters of equal height but widths containing fractional parts including 1/16,

1/8, 1/4, 1/3, 1/2 (or any fractional part that can be measured by using a 12

inch ruler); long strips of fadeless paper or a roll of drywall tape; scissors;

glue

Strategy:

Review addition with mixed numbers, first at the board, then at the desk using

individual worksheets. When seatwork is complete pair the students. Using a

tape measure, each student will measure distance from his/her wrist to the tip

of the longest finger. Make a dot, with the marker, at that spot on the wrist

where the measurement began. Record the distance. Next, measure the distance

from the spot on the wrist to the inside fold in the arm where the forearm and

upper arm meet. Put a dot on that spot in the fold. Record that distance.

Measure the distance from the inside fold in the arm to the shoulder joint.

Record it. Sum the three measurements. Measure the distance from the shoulder

joint to the inside fold in the arm. Compare the added length to the measured

length.

In the second activity students will select the precut letters to form such

things as school name, first name or nickname. Students will measure the width

of each letter, allocate 1/4 of an inch space between each letter, and then add

all letter widths and spaces. Once the students have calculated the width of

letters and spaces they will cut fadeless paper or drywall tape to equal the

width of the calculated letters and spaces. Paste the letters onto the

fadeless paper or drywall tape.Performance Assessment:

In the first activity, if the students have measured and added correctly, the

sum of the three measurements should equal the distance measured from shoulder

joint to finger tip. In the second activity, the length of the fadeless paper

or drywall tape should be equal to the sum of the letters and spaces. Both

activities are self checking.Grading Rubric

If the error in measurement is within 1/4 of an inch a grade of A should be

awarded. If the error in measurement is within 1/2 of an inch a grade of B

should be awarded. If the error in measurement is within 1 inch a grade of C

should be awarded. If the error in measurement is within 1 1/2 of an inch a

grade of D should be awarded. If the error in measurement is greater the

activity should be redone.Conclusions:

This activity enables the student to put math concepts to practical use. It

also motivates the student to measure correctly. Finally, the self-checking

mechanism makes the activities easy to grade.