`a, 3/8 + 7/12 + 10/16 + 10/24`
`= 3/8 + 7/12 + 5/8 + 5/12`
`= (3/8 + 5/8) + (7/12 + 5/12)`
`= 1 + 1`
`= 2`
`b, 5/7 xx 9/16 + 7/16 xx 5/7`
`= 5/7 xx (9/16 + 7/16)`
`= 5/7 xx 1`
`= 5/7`
`c, 4/6 + 7/13 + 17/9 + 19/13 + 1/9 + 14/6`
`= (4/6 + 14/6) + (7/13 + 19/13) + (17/9 + 1/9)`
`= 18/6 + 26/13 + 18/9`
`= 3 + 2 + 2`
`= 7`
`d, (2006 xx 2005 - 1)/(2004 xx 2006 + 2005)`
`= (2006 xx (2004 + 1) - 1)/(2004 xx 2006 + 2005)`
`= (2006 xx 2004 + 2006 xx 1 - 1)/(2004 xx 2006 + 2005)`
`= (2006 xx 2004 + (2006 - 1))/(2004 xx 2006 + 2005)`
`= (2006 xx 2004 + 2005)/(2004 xx 2006 + 2005)`
`= 1`
