He has £160 out of £400 saved up. Just rewrite that as a fraction and then there are two ways to finish it off.
The first way would be to just divide. [tex] \frac{160}{400}=.4[/tex] Then turn that decimal into a percentage by multiplying by 100. [tex].4(100)=40[/tex] 40%
The second way would be simplify the fraction until the denominator is 100. The numerator is your answer. [tex] \frac{160}{400}=\frac{40}{100}[/tex] 40%