1. จงหาผลลัพธ์
1) \(\mathsf{\frac{2}{5} \div (-3)}\)
วิธีทำ
\(\mathsf{\frac{2}{5} \div (-3)}\) = \(\mathsf{\frac{2}{5} \times (-\frac{1}{3})}\)
= \(\mathsf{\frac{2 \, \times \, (-1)}{5 \, \times \, 3}}\)
= \(\mathsf{-\frac{2}{15}}\)
ตอบ \(\mathsf{-\frac{2}{15}}\)
2) \(\mathsf{(-6) \div \frac{1}{3}}\)
วิธีทำ
\(\mathsf{(-6) \div \frac{1}{3}}\) = (-6) x 3
= -18
ตอบ -18
3) \(\mathsf{(-\frac{5}{7}) \div (-\frac{4}{9})}\)
วิธีทำ
\(\mathsf{(-\frac{5}{7}) \div (-\frac{4}{9})}\) = \(\mathsf{(-\frac{5}{7}) \times (-\frac{9}{4})}\)
= \(\mathsf{\frac{(-5) \, \times \, (-9)}{7 \, \times \, 4}}\)
= \(\mathsf{\frac{45}{28}}\)
= \(\mathsf{1\frac{17}{28}}\)
ตอบ \(\mathsf{1\frac{17}{28}}\)
4) \(\mathsf{(-4\frac{2}{3}) \div 6}\)
วิธีทำ
\(\mathsf{(-4\frac{2}{3}) \div 6}\) = \(\mathsf{(-\frac{14}{3}) \times \frac{1}{6}}\)
= \(\mathsf{(-\frac{14^7\mkern-18mu\color{Red}/}{3}\,) \times \frac{1}{6_3\mkern-15mu\color{Red}/}}\)
= \(\mathsf{(-\frac{7}{3}) \times \frac{1}{3}}\)
= \(\mathsf{\frac{(-7) \, \times \, 1}{3 \, \times \, 3}}\)
= \(\mathsf{-\frac{7}{9}}\)
ตอบ \(\mathsf{-\frac{7}{9}}\)
5) \(\mathsf{3\frac{1}{11} \div (-2\frac{19}{33})}\)
วิธีทำ
\(\mathsf{3\frac{1}{11} \div (-2\frac{19}{33})}\) = \(\mathsf{\frac{34}{11} \div (-\frac{85}{33})}\)
= \(\mathsf{\frac{34}{11} \times (-\frac{33}{85})}\)
= \(\mathsf{\frac{34^2\mkern-18mu\color{Red}/}{11_1\mkern-18mu\color{Magenta}/} \times (-\frac{33^3\mkern-18mu\color{Magenta}/}{85_5\mkern-18mu\color{Red}/}\;)}\)
= \(\mathsf{\frac{2}{1} \times (-\frac{3}{5})}\)
= \(\mathsf{\frac{2 \, \times \, (-3)}{1 \, \times \, 5}}\)
= \(\mathsf{-\frac{6}{5}}\)
= \(\mathsf{-1\frac{1}{5}}\)
ตอบ \(\mathsf{-1\frac{1}{5}}\)
6) \(\mathsf{\frac{1}{4}[(-\frac{4}{5}) \div (-1\frac{1}{2})]}\)
วิธีทำ
\(\mathsf{\frac{1}{4}[(-\frac{4}{5}) \div (-1\frac{1}{2})]}\) = \(\mathsf{\frac{1}{4}[(-\frac{4}{5}) \div (-\frac{3}{2})]}\)
= \(\mathsf{\frac{1}{4}[(-\frac{4}{5}) \times (-\frac{2}{3})]}\)
= \(\mathsf{\frac{1}{4} \times (-\frac{4}{5}) \times (-\frac{2}{3})}\)
= \(\mathsf{\frac{1}{4_1\mkern-15mu\color{Red}/} \times (-\frac{4^1\mkern-15mu\color{Red}/}{5}) \times (-\frac{2}{3})}\)
= \(\mathsf{1 \times (-\frac{1}{5}) \times (-\frac{2}{3})}\)
= \(\mathsf{\frac{(-1 \, \times \, (-2)}{5 \, \times \, 3}}\)
= \(\mathsf{\frac{2}{15}}\)
ตอบ \(\mathsf{\frac{2}{15}}\)
7) \(\mathsf{(2\frac{3}{4} \times \frac{5}{6}) \div \frac{11}{12}}\)
วิธีทำ
\(\mathsf{(2\frac{3}{4} \times \frac{5}{6}) \div \frac{11}{12}}\) = \(\mathsf{(\frac{11}{4} \times \frac{5}{6}) \times \frac{12}{11}}\)
= \(\mathsf{(\frac{11^1\mkern-18mu\color{Red}/}{4_1\mkern-15mu\color{Magenta}/} \times \frac{5}{6}) \times \frac{12^3\mkern-18mu\color{Magenta}/}{11_1\mkern-18mu\color{Red}/}}\)
= \(\mathsf{1 \times \frac{5}{6} \times 3}\)
= \(\mathsf{\frac{5}{6_2\mkern-15mu\color{Red}/} \times 3^1\mkern-16mu\color{Red}/}\)
= \(\mathsf{\frac{5}{2}}\)
= \(\mathsf{2\frac{1}{2}}\)
ตอบ \(\mathsf{2\frac{1}{2}}\)
8) \(\mathsf{[(-\frac{2}{5}) \div \frac{8}{21}](-\frac{3}{7})}\)
วิธีทำ
\(\mathsf{[(-\frac{2}{5}) \div \frac{8}{21}](-\frac{3}{7})}\) = \(\mathsf{[(-\frac{2}{5}) \times \frac{21}{8}](-\frac{3}{7})}\)
= \(\mathsf{(-\frac{2}{5}) \times \frac{21}{8} \times (-\frac{3}{7})}\)
= \(\mathsf{(-\frac{2^1\mkern-15mu\color{Red}/}{5}) \times \frac{21^3\mkern-18mu\color{Magenta}/}{8_4\mkern-15mu\color{Red}/} \times (-\frac{3}{7_1\mkern-16mu\color{Magenta}/})}\)
= \(\mathsf{(-\frac{1}{5}) \times \frac{3}{4} \times (-3)}\)
= \(\mathsf{\frac{(-1) \, \times \, 3 \, \times \, (-3)}{5 \, \times \, 4}}\)
= \(\mathsf{\frac{9}{20}}\)
ตอบ \(\mathsf{\frac{9}{20}}\)
9) \(\mathsf{(-\frac{9}{10}) \div (\frac{1}{6} + \frac{2}{3})}\)
วิธีทำ
\(\mathsf{(-\frac{9}{10}) \div (\frac{1}{6} + \frac{2}{3})}\) = \(\mathsf{(-\frac{9}{10}) \div [\frac{1}{6} + (\frac{2}{3} \times \frac{2}{2})]}\)
= \(\mathsf{(-\frac{9}{10}) \div (\frac{1}{6} + \frac{4}{6})}\)
= \(\mathsf{(-\frac{9}{10}) \div \frac{5}{6}}\)
= \(\mathsf{(-\frac{9}{10}) \times \frac{6}{5}}\)
= \(\mathsf{(-\frac{9}{10_5\mkern-18mu\color{Red}/}\;) \times \frac{6^3\mkern-15mu\color{Red}/}{5}}\)
= \(\mathsf{(-\frac{9}{5}) \times \frac{3}{5}}\)
= \(\mathsf{\frac{(-9) \, \times \, 3}{5 \, \times \, 5}}\)
= \(\mathsf{-\frac{27}{25}}\)
= \(\mathsf{-1\frac{2}{25}}\)
ตอบ \(\mathsf{-1\frac{2}{25}}\)
10) \(\mathsf{(-3\frac{1}{2}) \div (2\frac{1}{8} \; – \, \frac{3}{4})}\)
วิธีทำ
\(\mathsf{(-3\frac{1}{2}) \div (2\frac{1}{8} \; – \, \frac{3}{4})}\) = \(\mathsf{(-\frac{7}{2}) \div (\frac{17}{8} \; – \, \frac{3}{4})}\)
= \(\mathsf{(-\frac{7}{2}) \div [(\frac{17}{8} \; – \, (\frac{3}{4} \times \frac{2}{2})]}\)
= \(\mathsf{(-\frac{7}{2}) \div (\frac{17}{8} \; – \, \frac{6}{8})}\)
= \(\mathsf{(-\frac{7}{2}) \div \frac{11}{8}}\)
= \(\mathsf{(-\frac{7}{2}) \times \frac{8}{11}}\)
= \(\mathsf{(-\frac{7}{2_1\mkern-15mu\color{Red}/}) \times \frac{8^4\mkern-15mu\color{Red}/}{11}}\)
= \(\mathsf{(-7) \times \frac{4}{11}}\)
= \(\mathsf{\frac{(-7) \, \times \, 4}{11}}\)
= \(\mathsf{-\frac{28}{11}}\)
= \(\mathsf{-2\frac{6}{11}}\)
ตอบ \(\mathsf{-2\frac{6}{11}}\)