p(student fails in Physics)=p(E)$=30\%=\large\frac{30}{100}$
p(student fails in Mathematics)=p(F)$=25\%=\large\frac{25}{100}$
p(fails both in Physics and Mathematics)$=p(E\cap F)=10\%=\large\frac{10}{100}$
p(Fails in Physics given tails in Mathmatics)
$p(E/F)=\Large\frac{p(E\cap F)}{p(F)}$
=$\Large\frac{10/100}{25/100}$
=$\Large\frac{2}{5}$