Câu 2. Tính:

a) \( \frac{3}{4}+\frac{2}{3}+\frac{5}{12}\) ;        b) \( \frac{7}{8}-\frac{7}{16}-\frac{11}{32}\);          

c) \( \frac{3}{5}\times\frac{2}{7}\times\frac{5}{6}\) ;        d) \( \frac{15}{16}:\frac{3}{8}\times\frac{3}{4}\)

Giải

a) \( \frac{3}{4}+\frac{2}{3}+\frac{5}{12}={9 \over {12}} + {8 \over {12}} + {5 \over {12}} = {{22} \over {12}} = {{11 \times 2} \over {6 \times 2}} = {{11} \over 6}\);

b) \( \frac{7}{8}-\frac{7}{16}-\frac{11}{32}={{28} \over {32}} - {{14} \over {32}} - {{11} \over {32}} = {3 \over {32}}\);

c) \( \frac{3}{5}\times\frac{2}{7}\times \frac{5}{6}\) \( =\frac{3\times2\times5}{5\times7\times6}=\frac{3\times2\times5}{5\times7\times2\times 3}=\frac{1}{7}\) ;

 d) \( \frac{15}{16}:\frac{3}{8}\times\frac{3}{4}\) \( =\frac{15}{16}\times\frac{8}{3}\times\frac{3}{4} = {{15 \times 8 \times 3} \over {16 \times 3 \times 4}} \)

     \(= {{15 \times 8 \times 3} \over {2 \times 8 \times 3 \times 4}} = {{15} \over 8}\).