Ответ:
\[3\frac{12}{17}+2\frac{5}{17}=5\frac{17}{17}=6.\]
\[15:6=2.5.\]
\[4.2-2\frac{3}{5}=4.2-2.6=1.6,\qquad 1.6:4=0.4.\]
\[2.5+0.4=2.9.\]
Ответ: 2,9.
\[3\frac{12}{17}+2\frac{5}{17}=5\frac{17}{17}=6.\]
\[15:6=2.5.\]
\[4.2-2\frac{3}{5}=4.2-2.6=1.6,\qquad 1.6:4=0.4.\]
\[2.5+0.4=2.9.\]
Ответ: 2,9.