6道简便用算

6道简便用算

6道简便计算题（简便方法）
可能有不能用简便算法的,
(1/39+2/35)×13+9/35
4/5+(2/3-4/7)×21/2
17/35×3/11+8/35÷11/17
(1/10+1/17)×13+4÷17
62.5％×15+2×5/8-5÷8
2008又1/2006×2006/2007

(1/39+2/35)×13+9/35 =1/3+26/35+9/35 =1/3+1=1又1/3
4/5+(2/3-4/7)×21/2=4/5+7-6=1又4/5
17/35×3/11+8/35÷11/17=17/35×3/11+8/35×17/11=17/35×(3/11+8/11)=17/35
(1/10+1/17)×13+4÷17=13/10+13/17+4/17=13/10+1=2.3
62.5％×15+2×5/8-5÷8=5/8×15+2×5/8-5/8=5/8×(15+2-1)=5/8×16=10
2008又1/2006×2006/2007=(2008×2006+1)/2007=[(2007+1)(2007-1)+1]/2007=(2007^2)/2007=2007