[tex]1. \: \: 20 + ( - 4 \times 5) - 7 \\ 20 + ( - 20) - 7 \\ 20 - 20 - 7 \\ - 7[/tex]
[tex]2. \: \: 3.6 - 1 \frac{2}{3} + 0.2 = \frac{36}{10} - \frac{5}{3} + \frac{2}{10} \\ \\ = \frac{18}{5} - \frac{5}{3} + \frac{1}{5} = \frac{54 - 25 + 3}{15} = \frac{32}{15} = 2 \frac{2}{15} = 2.13[/tex]
[tex]3. \: \: 4.3 \times 1.2 = \frac{43}{10} \times \frac{12}{10} = \frac{43}{10} \times \frac{6}{5} \\ \\ = \frac{258}{50} = \frac{129}{25} = 5 \frac{4}{25} = 5.16[/tex]
[tex]4. \: \: 0.4 \times 2.1 = \frac{4}{10} \times \frac{21}{10} \\ \\ = \frac{2}{5} \times \frac{21}{10} = \frac{42}{50} = \frac{21}{25} = 0.84[/tex]
[tex]5. \: \: 3.3 \div 1.5 = \frac{33}{10} \div \frac{15}{10} = \frac{33}{10} \div \frac{3}{2} \\ \\ = \frac{33}{10} \times \frac{2}{3} = \frac{11}{5} = 2 \frac{1}{5} = 2.2[/tex]
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