When expressing one quantity as a fraction of the other, the quantity which comes immediately after of will be our denominator.and the other is our numerator.
When dealing with rates, we must always work in the same unit.
For this particular question, you can decide to convert everything to Pounds or Pence.
So let us convert fifty Pence to Pounds.
[tex]100\: Pence= 1\: Pound[/tex]
[tex]\Rightarrow 50\; Pence =\frac{50}{100}\: Pounds[/tex]
[tex]\Rightarrow 50\; Pence =0.5 \: Pounds[/tex]
Now fifty Pence of £3.00 Pounds
[tex]=\frac{0.5}{3.00}[/tex]
[tex]=\frac{\frac{1}{2} }{3}[/tex]
[tex]=\frac{1}{6}[/tex]