7/13×8/17×5/13×2/17
=(7×8+5×2)/(13×17)
=66/221
11/3+11/15+11/35+11/63+11/99
=11/2×(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)
=11/2×(1-1/11)
=11/2×10/11
=5
7/13×8/17×5/13×2/17
=(7×8+5×2)/(13×17)
=66/221
11/3+11/15+11/35+11/63+11/99
=11/2×(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)
=11/2×(1-1/11)
=11/2×10/11
=5