用简便方法计算(1)(-3.14)x13/8+0.314x25/4-31.4x0.2(2)-150x(1/8)-25x0.125+50x(-1/4)(3)-1.99x17(4)31/2x(-5/7)-(-5/7)x21/2-5/7x(-1/2)(5)-13x2/3-0.34x2/7+1/3x(-13)-5/7x0.34

Question

用简便方法计算 ( 1) (-3.14)x 1 3/8+0.314x 25/4 -31.4 x 0.2 ( 2) -150 x (1/8) -25x0.125+50x(-1/4) (3) -1.99x17 (4) 3 1/2 x (-5/7) - (-5/7) x 2 1/2 - 5/7 x (-1/2) (5) -13 x 2/3 -0.34 x 2/7 + 1/3 x (-13) - 5/7 x 0.34

Answer 1

用简便方法计算：
( 1) (-3.14)x 1 3/8+0.314x 25/4 -31.4 x 0.2
=3.14*（-13/8+25/40-2)
=3.14*(-3)
=- 9.42
( 2) -150 x (1/8) -25x0.125+50x(-1/4)
=-25*(3/4+1/8+1/2)
=-25*11/8
=-25*(1+3/8)
=-25-75/8
=-34又3/8
(3) -1.99x17
=(0.01-2 )*17
=0.17-34
=-33.83
(4) 3 1/2 x (-5/7) - (-5/7) x 2 1/2 - 5/7 x (-1/2)
=(-5/7)*(31/2-21/2-1/2)
=-5/7*9/2
=-45/14
(5) -13 x 2/3 -0.34 x 2/7 + 1/3 x (-13) - 5/7 x 0.34
=[-13 x 2/3 + 1/3 x (-13) ]- [5/7 x 0.34+0.34 x 2/7]
=-13-0.34
=-13.34