Đáp án:
$a) \dfrac{13}{12}\\ b)\dfrac{7}{8} \\ c) \dfrac{9}{20} \\ d) \dfrac{5}{3}.$
Giải thích các bước giải:
$a) \dfrac{2}{8} + \dfrac{5}{6}\\ = \dfrac{1\times 2}{4 \times 2} + \dfrac{5}{6}\\ = \dfrac{1}{4} + \dfrac{5}{6}\\ = \dfrac{1 \times 3}{4\times 3} + \dfrac{5 \times 2}{6\times 2}\\ = \dfrac{3}{12} + \dfrac{10}{12}\\ =\dfrac{3+10}{12}\\ =\dfrac{13}{12}\\ b) \dfrac{1}{8} + \dfrac{12}{16}\\ =\dfrac{1}{8} + \dfrac{3 \times 4 }{4 \times 4} \\ =\dfrac{1}{8} + \dfrac{3 }{4} \\ =\dfrac{1}{8} + \dfrac{3\times 2 }{4 \times 2} \\ =\dfrac{1}{8} + \dfrac{6}{8} \\ =\dfrac{1+6}{8} \\ =\dfrac{7}{8} \\ c) \dfrac{1}{4} + \dfrac{6}{30}\\ =\dfrac{1}{4} + \dfrac{6}{6 \times 5} \\ =\dfrac{1}{4} + \dfrac{1}{5} \\ =\dfrac{1\times 5}{4\times 5} + \dfrac{1\times 4}{5\times 4} \\ =\dfrac{ 5}{20} + \dfrac{4}{20} \\ =\dfrac{ 5+4}{20} \\ =\dfrac{9}{20} \\ d) \dfrac{12}{18} + \dfrac{12}{12}\\ = \dfrac{2 \times 6}{3 \times 6} +1\\ = \dfrac{2 }{3} +1\\ = \dfrac{2 }{3} +\dfrac{3}{3}\\ = \dfrac{2 +3}{3}\\ = \dfrac{5}{3}.$
