ВАРИАНТ 3 1. Найдите сумму: 1) $$9\frac{3}{4}+3\frac{1}{6}$$; 2) $$11\frac{7}{12}+6\frac{11}{18}$$; 3) $$7\frac{8}{15}+8\frac{17}{20}$$; 4) $$7\frac{3}{8}+9\frac{7}{16}+11\frac{7}{12}$$.

1. $$9\frac{3}{4}+3\frac{1}{6} = \frac{39}{4} + \frac{19}{6} = \frac{39 \cdot 3}{4 \cdot 3} + \frac{19 \cdot 2}{6 \cdot 2} = \frac{117}{12} + \frac{38}{12} = \frac{155}{12} = 12\frac{11}{12}$$
2. $$11\frac{7}{12}+6\frac{11}{18} = \frac{139}{12} + \frac{119}{18} = \frac{139 \cdot 3}{12 \cdot 3} + \frac{119 \cdot 2}{18 \cdot 2} = \frac{417}{36} + \frac{238}{36} = \frac{655}{36} = 18\frac{7}{36}$$
3. $$7\frac{8}{15}+8\frac{17}{20} = \frac{113}{15} + \frac{177}{20} = \frac{113 \cdot 4}{15 \cdot 4} + \frac{177 \cdot 3}{20 \cdot 3} = \frac{452}{60} + \frac{531}{60} = \frac{983}{60} = 16\frac{23}{60}$$
4. $$7\frac{3}{8}+9\frac{7}{16}+11\frac{7}{12} = \frac{59}{8} + \frac{151}{16} + \frac{139}{12} = \frac{59 \cdot 6}{8 \cdot 6} + \frac{151 \cdot 3}{16 \cdot 3} + \frac{139 \cdot 4}{12 \cdot 4} = \frac{354}{48} + \frac{453}{48} + \frac{556}{48} = \frac{1363}{48} = 28\frac{19}{48}$$

Ответ:

1. $$12\frac{11}{12}$$
2. $$18\frac{7}{36}$$
3. $$16\frac{23}{60}$$
4. $$28\frac{19}{48}$$