How many US dollars are equivalent to 70 UK pounds?

£ (UK)	$ (US)
1	1.25
70	$ x $

The amount of US dollars will be greater than 70. Therefore, from the numbers in the first row, we create the fraction that is greater than 1 (i.e. $ \frac{1.25}{1} $)

\begin{align} So \quad x & =\frac{1.25}{1}\ \times\ 70 \\ \\ & = $(US)\ 87.50 \\ \\ \end{align}

How many pounds are equivalent to 80 US dollars?

£(UK)	$(US)
1	1.25
$x $	80

The amount of UK pounds will be less than 80. Therefore, from the numbers in the first row, we create the fraction that is less than 1 (i.e. $ \frac{1}{1.25} $)

\begin{align} So \quad x & =\frac{1}{1.25}\ \times\ 80 \\ \\ & = £(UK)\ 64 \\ \\ \end{align}