Splitting Fractions in "Two"
2/5 can be written as the sum of two unique unit fractions. For example, 2/5 = 1/3 + 1/15. Try to find two unique unit fractions whose sum is 2/7. What about 2/11? 2/13? Is there a pattern?
(Source: Herb Wills, School Science and Mathematics.)

Extensions 
Consider all fractions of the form
where n is a positive integer. Which fractions of this form may be expressed as the sum of two different unit fractions?

Related External Resources 
No Matter What Shape Your Fractions are In
A geometric approach to fractions.
Visual Fractions [ java applet ]
A series of java programs using number lines to help visualize fractions and the operations on them.
Learn Fractions with Cuisenaire Rods 
A lesson plan using Cuisenaire rods to learn fractions.
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