a) \({3 \over 5} - {{ - 7} \over {10}} - {{13} \over { - 20}}\);
b) \({5 \over 6} + {{ - 3} \over 4} - {7 \over {18}}\);
c) \({3 \over {14}} - {5 \over { - 8}} + {{ - 1} \over 2}\);
d) \({1 \over 4} + {1 \over { - 6}} + {1 \over 3} + {{ - 1} \over 2}\);
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e) \({{ - 13} \over {20}} + {5 \over { - 12}} - {{ - 7} \over {15}}\);
f) \({{ - 1} \over 2} + {{11} \over {30}} + \left( {{{29} \over {42}} - {2 \over {35}}} \right)\).
\(\eqalign{ & a){3 \over 5} - {{ - 7} \over {10}} - {{13} \over { - 20}} = {3 \over 5} - {{ - 7} \over {10}} - {{ - 13} \over {20}} = {{12} \over {20}} - {{ - 14} \over {20}} - {{ - 13} \over {20}} = {{12 - ( - 14) - ( - 13)} \over {20}} = {{39} \over {20}}. \cr & b){5 \over 6} + {{ - 3} \over 4} - {7 \over {18}} = {{30} \over {36}} + {{ - 27} \over {36}} - {{14} \over {36}} = {{30 + ( - 27) - 14} \over {36}} = {{ - 11} \over {36}}. \cr & c){3 \over {14}} - {5 \over { - 8}} + {{ - 1} \over 2} = {{12} \over {56}} - {{ - 35} \over {56}} + {{ - 28} \over {56}} = {{12 - ( - 35) + ( - 28)} \over {56}} = {{19} \over {56}}. \cr & d){1 \over 4} + {1 \over { - 6}} + {1 \over 3} + {{ - 1} \over 2} = {3 \over {12}} + {{ - 2} \over {12}} + {4 \over {12}} + {{ - 6} \over {12}} = {{3 + ( - 2) + 4 + ( - 6)} \over {12}} = {{ - 1} \over {12}}. \cr & e){{ - 13} \over {20}} + {5 \over { - 12}} - {{ - 7} \over {15}} = {{ - 39} \over {60}} + {{ - 25} \over {60}} - {{ - 28} \over {60}} = {{ - 39 + ( - 25) - ( - 28)} \over {60}} = {{ - 36} \over {60}} = {{ - 3} \over 5}. \cr & f){{ - 1} \over 2} + {{11} \over {30}} + \left( {{{29} \over {42}} - {2 \over {35}}} \right) = {{ - 105} \over {210}} + {{77} \over {210}} + {{145} \over {210}} - {{12} \over {210}} = {{ - 105 + 77 + 145 - 12} \over {210}} = {{105} \over {210}} = {1 \over 2}. \cr} \)