简便计算,有点难
问题描述：
简便计算,有点难
1/4*3.5*5.4 / 0.9*3*2.5*4.9
2/3+2/15=2/35+2/63
1/1*2+1/2*3+1/3*4+.+1/99*100
答
2/3+2/15+2/35+2/63
=(2/3+2/15)+(2/35+2/63)
=4/5+28/315
=91/315
1/1*2+1/2*3+1/3*4+.+1/99*100
=1-1/2+1/2-1/3+1/3-1/4+……+1/99-1/100
=1-1/100
=99/1001/4*3.5*5.4/0.9*3*2.5*4. 这题呢