6/17×8/21+8/17×11/21
=8/17×6/21+8/17×11/21
=8/17×(6/21+11/21)
=8/17×17/21
=8/21
6/17×8/21+8/17×11/21
=8/17×6/21+8/17×11/21
=8/17×(6/21+11/21)
=8/17×17/21
=8/21
6/17×8/21+8/17×11/21
=8/21×(6/17+11/17)
=8/21×1
=8/21
6/17×8/21+8/17×11/21
=(6×8+8×11)/17×21
=8×17/17×21
=8/21