3/17 x 4/21 + 3/17 x 25/21 - 8/21 x 3/17 = 3/17 x ( 4/21 + 25/21 - 8) = 3/17 x 1= 3/17
\(\frac{3}{17}.\frac{4}{21}+\frac{3}{17}.\frac{25}{21}-\frac{8}{21}.\frac{3}{17}\)
\(=\frac{3}{17}\left(\frac{4}{21}+\frac{25}{21}-\frac{8}{21}\right)\)
\(=\frac{3}{17}.1\)
\(=\frac{3}{17}\)