计算下面三题5/7×2/5+1/4×4/724×2/7×5/72×215/7×8/13+2/13×8/7

计算下面三题5/7×2/5+1/4×4/724×2/7×5/72×215/7×8/13+2/13×8/7
计算下面三题
5/7×2/5+1/4×4/7
24×2/7×5/72×21
5/7×8/13+2/13×8/7

计算下面三题5/7×2/5+1/4×4/724×2/7×5/72×215/7×8/13+2/13×8/7
1原式=2/7+1/7=3/7
2原式=24x5/72x2/7x21=10
3原式=8/13x(5/7+2/7)=8/13