2,75^2:1\frac{5}{6}=7,5625:\frac{11}{6}=7,5625*\frac{6}{11}=\frac{45,375}{11}=4,125
420-20*\frac{3}{4}+6,25:(-5,80)=420-15+\frac{625}{100}:(-\frac{580}{100})=405-\frac{25}{4}:\frac{29}{5}=405-\frac{25}{4}*\frac{5}{29}=405-\frac{125}{116}=405-1\frac{9}{116}=403\frac{107}{116}
(\frac{1}{3}-0,25)^2+3^2=(\frac{1}{3}-\frac{1}{4})^2+9=(\frac{4}{12}-\frac{3}{12})^2+9=(\frac{1}{12})^2+9=\frac{1}{144}+9=9\frac{1}{144}
3^3-1\frac{1}{3}=27-1\frac{1}{3}=25\frac{2}{3}
4^2*2\frac{1}{3}=16*\frac{7}{3}=\frac{112}{3}=37\frac{1}{3}
\frac{1}{2}+3\frac{3}{4}=\frac{2}{4}+3\frac{3}{4}=3\frac{5}{4}=4\frac{1}{4}
3\frac{2}{7}*\frac{21}{4}=\frac{23}{7}*\frac{21}{4}=23*\frac{3}{4}=\frac{69}{4}=17,25
2\frac{3}{8}:\frac{2}{4}=\frac{19}{8}:\frac{1}{2}=\frac{19}{8}*2=\frac{38}{8}=4,75