(a) `2/3+ 4/3 = (2+4)/3 = 6/3 = 2`
`1/3 + 2/3 = (1+2)/3 = 1`
`2/3 - 1/3 = (2-1)/3 = 1/3`
`4/3 - 2/3 = (4-2)/3 = 2/3`
(b) `1/2 + 1/3 = 3/6 + 2/6 = (3+2)/6 = 5/6`
`1/3+1/4 = 4/12 + 3/12 = 7/12`
`1/2 - 1/3 = 3/6 - 2/6 = (3-2)/6 = 1/6`
`1/3 - 1/4 = 4/12 - 3/12 = (4-3)/12= 1/12`
`1/6 + 1/12 = 2/12+ 1/12`
`(2+1)/12= 3/12= 1/4`
`5/6 - 7/12 = 10/12- 7/12= (10-7)/12= 3/12=1/4`
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