Bài tập 119 trang 32 SBT Toán 6 Tập 2

Bài tập 119 trang 32 SBT Toán 6 Tập 2

\(\begin{array}{l}
a)4\frac{3}{4} + \left( { - 0,37} \right) + \frac{1}{8} + \left( { - 1,28} \right) + \left( { - 2,5} \right) + 3\frac{1}{{12}}\\
 = \left( {4\frac{3}{4} + \frac{1}{8} + 3\frac{1}{{12}}} \right) - \left( {0,37 + 1,28 + 2,5} \right)\\
 = 7\frac{{23}}{{24}} - 4,15\\
 = 7\frac{{23}}{{24}} - 4\frac{3}{{20}}\\
 = 3\frac{{97}}{{120}}\\
b)\frac{3}{{5.7}} + \frac{3}{{7.9}} + ... + \frac{3}{{59.61}}\\
 = \frac{3}{2}.\left( {\frac{2}{{5.7}} + \frac{2}{{7.9}} + .. + \frac{2}{{59.61}}} \right)\\
 = \frac{3}{2}.\left( {\frac{1}{5} - \frac{1}{7} + \frac{1}{7} - \frac{1}{9} + ... + \frac{1}{{59}} - \frac{1}{{61}}} \right)\\
 = \frac{3}{2}.\left( {\frac{1}{5} - \frac{1}{{61}}} \right)\\
 = \frac{3}{2}.\frac{{56}}{{305}} = \frac{{84}}{{305}}\\
c)\frac{{\frac{5}{{22}} + \frac{3}{{13}} - \frac{1}{2}}}{{\frac{4}{{13}} - \frac{2}{{11}} + \frac{3}{2}}}\\
 = \frac{{\left( {\frac{5}{{22}} + \frac{3}{{13}} - \frac{1}{2}} \right).\left( {2.11.13} \right)}}{{\left( {\frac{4}{{13}} - \frac{2}{{11}} + \frac{3}{2}} \right).\left( {2.11.13} \right)}}\\
 = \frac{{65 + 66 - 143}}{{88 - 52 + 429}}\\
 = \frac{{ - 12}}{{465}} = \frac{{ - 4}}{{155}}
\end{array}\)

-- Mod Toán 6