### Look Before You Leap

Relate these algebraic expressions to geometrical diagrams.

### Modular Fractions

We only need 7 numbers for modulus (or clock) arithmetic mod 7 including working with fractions. Explore how to divide numbers and write fractions in modulus arithemtic.

### All Tangled Up

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?