Решение:
$\frac{(1,75 : \frac{2}{3} - 1,75 \cdot 1\frac{1}{8}) : \frac{7}{12}}{(\frac{17}{80} - 0,0325): 400} : (6,79 : 0,7 + 0,3) = 250.$

$1) 1,75 : \frac{2}{3} = 1\frac{75}{100} \cdot \frac{3}{2} = 1\frac{3}{4} \cdot \frac{3}{2} = \frac{7}{4} \cdot \frac{3}{2} = \frac{7 \cdot 3}{4 \cdot 2} = \frac{21}{8} = 2\frac{5}{8};$

$2) 1,75 \cdot 1\frac{1}{8} = 1\frac{75}{100} \cdot \frac{9}{8} = 1\frac{3}{4} \cdot \frac{9}{8} = \frac{7}{4} \cdot \frac{9}{8} = \frac{7 \cdot 9}{4 \cdot 8} = \frac{63}{32} = 1\frac{31}{32};$

$3) 2\frac{5}{8} - 1\frac{31}{32} = 2\frac{20}{32} - 1\frac{31}{32} = 1 + 1 + \frac{20}{32} - 1\frac{31}{32} = 1 + \frac{32}{32} + \frac{20}{32} - 1\frac{31}{32} = 1 - 1 + \frac{32 + 20 - 31}{32} = \frac{21}{32};$

$4) \frac{21}{32} : \frac{7}{12} = \frac{21}{32} \cdot \frac{12}{7} = \frac{21 \cdot 12}{32 \cdot 7} = \frac{3 \cdot 3}{8 \cdot 1} = \frac{9}{8} = 1\frac{1}{8};$

$5) \frac{17}{80} - 0,0325 = \frac{17}{80} - \frac{325}{10000} = \frac{17}{80} - \frac{13}{400} = \frac{85}{400} - \frac{13}{400} = \frac{72}{400} = \frac{9}{50} = \frac{18}{100} = 0,18;$

$6) 0,18 : 400 = 0,00045;$

$7) 1\frac{1}{8} : 0,00045 = \frac{9}{8} : \frac{45}{100000} = \frac{9}{8} \cdot \frac{100000}{45} = \frac{9 \cdot 100000}{8 \cdot 45} = \frac{9 \cdot 12500}{1 \cdot 45} = \frac{112500}{45} = 112500 : 45 = 2500;$

$8) 6,79 : 0,7 = 9,7;$

$9) 9,7 + 0,3 = 10;$

$10) 2500 : 10 = 250.$
Ответ: 250.

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