Question

2.计算下面各题，注意使用简便算法。

2 3 7 3 1 3 1 11 9 4 1 3 1
—×（—+—） （—-—）÷（—+—） —- — - — 【1-（—+—）】÷—
5 4 8 4 9 4 9 9 13 13 4 8 4

Answer 1

2/5 X ( 3/4 + 7/8 )
= 8/20 X ( 3/4 + 7/8 )
= ( 8 X 3/4 + 8 X 7/8 ) / 20
= ( 2X3 + 7 ) / 20
= ( 6 + 7 ) / 20
= 13 /颤模20

( 3/4 - 1/9 ) / ( 3/4 + 1/9 )
= 36 X ( 3/历敬4 - 1/9 ) / ( 3/4 + 1/9 ) X 36
= ( 9X3 - 4 ) / ( 9X3 + 4 )
= ( 27 - 4 ) / ( 27 + 4 )
= 23 /31

11/9 - 9/13 - 4/13
= 11/茄烂缓9 - ( 9/13 + 4/13 )
= 2/9 + 9/9 - 13/13
= 2 /9

[ 1 - ( 1/4 + 3/8 ) ] / ( 1/4 )
= [ 1 - 1/4 - 3/8 ] X 4
= [ 3/4 - 3/8 ] X 4
= 4 X 3/4 - 4 X 3/8
= 3 - 3/2
= 1.5