[tex]a)\ \frac{1+2+3+4}{15} =\frac{10}{15} =\frac{2}{3} \\b)\frac{3+1+21}{100} =\frac{25}{100}=\frac{1}{4} \\\\\\a)\frac{2*4+3+1*5+7*2}{20}=\frac{8+3+5+14}{20} =\frac{30}{20} =\frac{3}{2}[/tex]
