a) $21\%=0.21$

$11.3\%=0.113$

$4.13\%=0.0413$

$160\%=1.6$

$0.5\%=0.005$

$3.5\%=0.035$

b) $15\%=\frac{15}{100}=\frac{3}{20}$

$24\%=\frac{24}{100}=\frac{6}{25}$

$80\%=\frac{80}{100}=\frac{4}{5}$

$48\%=\frac{48}{100}=\frac{12}{25}$

$120\%=\frac{120}{100}=1\frac{1}{5}$

$32.5\%=\frac{325}{1000}=\frac{13}{40}$