Обчисли:
Розв'язок:
1) $2\frac{3}{7} + \left(-3\frac{1}{2}\right) - 5\frac{9}{14} =$
$= 2\frac{3}{7} + \left(-3\frac{1}{2}\right) + \left(-5\frac{9}{14}\right) =$
$= 2\frac{3}{7} + \left(-8\frac{7+9}{14}\right) = 2\frac{3}{7} + \left(-8\frac{16}{14}\right) =$
$= -\left(8\frac{8}{7} - 2\frac{3}{7}\right) = -6\frac{5}{7}$;
2) $4\frac{2}{9} - 5\frac{1}{18} - \left(-1\frac{5}{6}\right) + \left(-\frac{2}{3}\right) =$
$= 4\frac{2}{9} + \left(-5\frac{1}{18}\right) + 1\frac{5}{6} + \left(-\frac{2}{3}\right) =$
$= 5\frac{4+15}{18} + \left(-5\frac{1+12}{18}\right) =$
$= 5\frac{19}{18} + \left(-5\frac{13}{18}\right) = \frac{6}{18} = \frac{1}{3}$;
3) $-3\frac{1}{2} + 4{,}8 - 8{,}7 - \left(-5\frac{1}{5}\right) =$
$= -3{,}5 + 4{,}8 + (-8{,}7) + 5{,}2 =$
$= 10 + (-12{,}2) = -2{,}2$;
4) $7{,}8 - 9\frac{1}{4} - 4\frac{7}{10} - (-3{,}4) =$
$= 7{,}8 + (-9{,}25) + (-4{,}7) + 3{,}4 =$
$= 11{,}2 + (-13{,}95) = -2{,}75$.