279. Выполните вычитание: 1) 3 1/12 - 1 1/6; 2) 8 7/30 - 2 9/20; 3) 7 10/51 - 4 21/34; 4) 5 1/4 - 1 3/8.

Решение:

1. \( 3 \frac{1}{12} - 1 \frac{1}{6} = \frac{37}{12} - \frac{7}{6} = \frac{37}{12} - \frac{14}{12} = \frac{23}{12} = 1 \frac{11}{12} \)
2. \( 8 \frac{7}{30} - 2 \frac{9}{20} = \frac{247}{30} - \frac{49}{20} = \frac{494}{60} - \frac{147}{60} = \frac{347}{60} = 5 \frac{47}{60} \)
3. \( 7 \frac{10}{51} - 4 \frac{21}{34} = \frac{367}{51} - \frac{157}{34} = \frac{734}{102} - \frac{471}{102} = \frac{263}{102} = 2 \frac{59}{102} \)
4. \( 5 \frac{1}{4} - 1 \frac{3}{8} = \frac{21}{4} - \frac{11}{8} = \frac{42}{8} - \frac{11}{8} = \frac{31}{8} = 3 \frac{7}{8} \)

Ответ: 1) \( 1 \frac{11}{12} \); 2) \( 5 \frac{47}{60} \); 3) \( 2 \frac{59}{102} \); 4) \( 3 \frac{7}{8} \).