Resposta:
[tex]a)\\ {4\over5}+{1\over2}-{5\over8}=\\ \\ mmc(5,2,8)=40\\ \\ {32+20-25\over40}=\\ \\ {52-25\over40}={27\over40}[/tex]
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[tex]b)\\ {1\over2}+{1\over4}-{1\over8}=\\ \\ mmc(2,4,8)=8\\ \\ {4+2-1\over8}={5\over8}[/tex]
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[tex]c)\\ 1{1\over2}+2-{9\over10}=\\ \\ {3\over2}+2-{9\over10}=\\ \\ mmc(2,10)=10\\ \\ {15+20-9\over10}=\\ \\ {35-9\over10}={26\over10}=\to simplificando ~{26:2\over10:2}={13\over5}[/tex]
