\[3\frac{2}{5}+1\frac{3}{4}=4+\left(\frac{2}{5}+\frac{3}{4}\right)=4+\frac{8}{20}+\frac{15}{20}=4\frac{23}{20}=5\frac{3}{20}.\]
Ответ: \(5\frac{3}{20}\).