[tex]12. \\\\a) \\\frac12+\frac38=\frac48+\frac38=\frac78\\\frac23+\frac35=\frac{10}{15}+\frac{9}{15}=\frac{13}{15}\\\frac{3}{10}+\frac{3}{4}=\frac6{20}+\frac{15}{20}=\frac{21}{20}=1\frac1{20}\\\\b) \\2\frac3{10}+\frac12=2\frac3{10}+\frac5{10}=2\frac8{10}=2\frac{4}5\\\frac23+3\frac16=\frac46+3\frac16=3\frac56\\2\frac37+\frac34=2\frac{12}{28}+\frac{21}{28}=2\frac{33}{28}=3\frac{5}{28}\\[/tex]
[tex]c)\\\frac23+2\frac59=\frac69+2\frac59=2\frac{11}9=3\frac29\\2\frac27+1\frac12=2\frac{4}{14}+1\frac{7}{14}=3 \frac{11}{14}\\1\frac56+2\frac38=1\frac{20}{24}+2\frac{9}{24}=3\frac{29}{24}=4\frac5{24}[/tex]
[tex]13. \\a) \\\frac9{10}-\frac35=\frac9{10}-\frac6{10}=\frac3{10}\\\frac56-\frac34=\frac{10}{12}-\frac{9}{12}=\frac1{12}\\\frac34-\frac29=\frac{27}{36}-\frac{8}{36}=\frac{19}{36}[/tex]
[tex]b) \\1\frac12-\frac25=1\frac5{10}-\frac4{10}=1\frac1{10}\\2\frac58-1\frac14=2\frac58-1\frac28=1\frac38\\3\frac34-1\frac16=3\frac{9}{12}-1\frac{2}{12}=2\frac7{12}[/tex]
[tex]c)\\1\frac15-\frac12=1\frac2{10}-\frac5{10}=\frac{12}{10}-\frac5{10}=\frac7{10}\\1\frac14-\frac35=1\frac{5}{20}-\frac{12}{20}=\frac{25}{20}-\frac{12}{20}=\frac{13}{20}\\2\frac23-\frac34=2\frac{8}{12}-\frac{9}{12}=1\frac{20}{12}-\frac9{12}=1\frac{11}{12}[/tex]
