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Relate these algebraic expressions to geometrical diagrams.

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Can you tangle yourself up and reach any fraction?

Can it Be

Age 16 to 18 Challenge Level:

When, if ever, is $${a\over b} + {c\over d} = {a+c\over b+d}$$ where $a$ and $b$ have no factors in common and $c$ and $d$ have no factors in common?
The NRICH Project aims to enrich the mathematical experiences of all learners. To support this aim, members of the NRICH team work in a wide range of capacities, including providing professional development for teachers wishing to embed rich mathematical tasks into everyday classroom practice.
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