`a) 6 1/3 : 1 6/11 - 1 2/17 xx 1 1/3`
`= 19/3 : 17/11 - 19/17 xx 4/3`
`= 19/3 xx 11/17 - 19/17 xx 4/3`
`=209/51 - 76/51`
`= 133/51`
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`b) 2 1/7 + 3 1/5 xx 2 1/2`
`= 15/7 + 16/5 xx 5/2`
`= 15/7 + 8`
`= 15/7 + 56/7`
`= 71/7`
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`c) 2 2/3 xx 1 1/5 + 2 2/3xx 2 1/5 + 2 2/3 xx 3 1/5`
`= 8/3 xx 6/5 + 8/3 xx 11/5 + 8/3 xx 16/5`
`= 8/3 xx ( 6/5 + 11/5 + 16/5)`
`= 8/3 xx 33/5`
`= 88/5`