Ответ:

  1. а) \(\frac47x+\frac5{14}x=(\frac8{14}+\frac5{14})x=\frac{13}{14}x\). При \(x=5\frac14=\frac{21}{4}\): \(\frac{13}{14}\cdot\frac{21}{4}=\frac{39}{8}=4\frac78\). При \(x=\frac9{13}\): \(\frac{13}{14}\cdot\frac9{13}=\frac9{14}\).
  2. б) \(\frac5{16}y+y-\frac38y=(\frac5{16}+\frac{16}{16}-\frac6{16})y=\frac{15}{16}y\). При \(y=1\frac1{15}=\frac{16}{15}\): значение равно 1. При \(y=1\frac78=\frac{15}{8}\): \(\frac{15}{16}\cdot\frac{15}{8}=\frac{225}{128}=1\frac{97}{128}\).
  3. в) \(\frac{17}{42}c-\frac27c+\frac7{18}c=(\frac{51}{126}-\frac{36}{126}+\frac{49}{126})c=\frac{32}{63}c\). При \(c=3\frac12=\frac72\): \(\frac{32}{63}\cdot\frac72=\frac{16}{9}=1\frac79\). При \(c=2\frac58=\frac{21}{8}\): \(\frac{32}{63}\cdot\frac{21}{8}=\frac43=1\frac13\).
  4. г) \(\frac34n+\frac23n-\frac4{18}n=(\frac{27}{36}+\frac{24}{36}-\frac8{36})n=\frac{43}{36}n\). При \(n=1\frac{13}{23}=\frac{36}{23}\): значение равно \(\frac{43}{23}=1\frac{20}{23}\). При \(n=\frac6{41}\): \(\frac{43}{36}\cdot\frac6{41}=\frac{43}{246}\).