First of all, find the GCF. (Greatest common factor.)
Which is 7. Meaning that 7 is the only number that can go into 7 itself and 28.
Now divide both the numerator and denominator (top and bottom number) by 7.
[tex] \sf \dfrac{7 \div 7}{28 \div 7} = \dfrac{1}{4} [/tex]