3. а) 2 3/4 : 1 1/10 + 1 1/10 : 2 3/4; б) 3,75 : 3 + 86,45 : 24,7;

а) \(2\frac{3}{4}:1\frac{1}{10}=\frac{11}{4}:\frac{11}{10}=\frac{5}{2}\).

\(1\frac{1}{10}:2\frac{3}{4}=\frac{11}{10}:\frac{11}{4}=\frac{2}{5}\).

\(\frac{5}{2}+\frac{2}{5}=\frac{29}{10}=2\frac{9}{10}\).

б) \(3.75:3+86.45:24.7=1.25+3.5=4.75\).

Ответ: а) \(2\frac{9}{10}\); б) \(4,75\).