\(\displaystyle a)\,\,{{ - 2} \over 3} + {4 \over {15}} = {{ - 2.5} \over {3.5}} + {4 \over {15}} \)\(\displaystyle = {{ - 10} \over {15}} + {4 \over {15}} = {{ - 10 + 4} \over {15}} \)\(\displaystyle = {{ - 6} \over {15}}= {{ -2} \over {5}}\)
\(\displaystyle b)\,\,{{11} \over {15}} + {9 \over { - 10}} \)\(\displaystyle = {{11.2} \over {15.2}} + {{9.( - 3)} \over { - 10.( - 3)}} \)\(\displaystyle = {{22} \over {30}} + {{ - 27} \over {30}} = {{22 + ( - 27)} \over {30}} \)\(\displaystyle = {{ - 5} \over {30}}= {{ - 1} \over {6}}\)\(\displaystyle c)\,\,{1 \over { - 7}} + 3 = {1 \over { - 7}} + {{ - 21} \over { - 7}} = {{1 + ( - 21)} \over { - 7}} \)\(\displaystyle = {{ - 20} \over { - 7}} = {{20} \over 7} \)
