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