用简便方法计算下面各题（1） 1/12÷1/4+11/12+3/4 （2） 29/30-1/6+1/30÷1/6 （3）

1/12 / 1/4 + 11/12 + 3/4
= 1/12 X 4 + 8/12 + 3/12 + 3/4
= 4/12 + 8/12 + 1/4 + 3/4
= 12/12 + 4/4
= 2
29/30 - 1/6 + 1/30 / 1/6
= 24/30 + 5/30 - 1/6 + 1/30 X 6
= 24/30 + 1/6 - 1/6 + 6/30
= 30/30
= 1
( 12/21 / 5/7 ) X ( 12/25 / 4/5 )
= 12/21 X 7/5 X 12/25 X 5/4
= ( 12 X 7 X 12 X 5 ) / ( 21 X 5 X 25 X 4 )
= ( 12 X 7 X 3 X 4 X 5 ) / ( 7 X 3 X 5 X 4 X 25 )
= 12/25
或者
= [ ( 21 X 12/21 ) / ( 5/7 X 21 ) ] X [ ( 25 X 12/25 ) / ( 4/5 X 25 ) ]
= [ 12 / ( 5 X 3 ) ] X [ 12 / ( 4 X 5 ) ]
= 4/5 X 3/5
= 12/25
5/17 / 9 + 1/9 X 4/17
= 5/17 X 1/9 + 1/9 X 4/17
= 1/9 X 9/17
= 1/17