Here is an activity where the students will be drawing,measuring, adding fractions and mixed numbers. The lesson will develop their ability to read a ruler and understand the concept of "error of measurement". Print slides 3 and 4 as full page handouts. Run these back to back and have the student draw the segments on the front, then measure to determine the length. Following, the students will turn the handout over and add the lengths to justify their answers. Measurements will range from half inch to sixteenth of an inch.
P.S. If there is interest, I can later post similar lessons dealing with the three other operations. Just let me know.