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3) 3.2 + 1.12 - 1.4 = 2.92

4) 1.4 < 2 < $2\frac{2}{7}$

1.4 < $\frac{11}{7}$ < $\frac{16}{7}$ (11/7 около 1.57)

5) $x + 3\frac{4}{21} = 4 \frac{5}{14} + 5 \frac{1}{12} \\\\x + \frac{67}{21} = \frac{61}{14} + \frac{61}{12} \\\\x + \frac{67}{21} = \frac{366+427}{84} = \frac{793}{84}\\\\ x = \frac{793}{84} - \frac{268}{84} = \frac{525}{84} = 6\frac{21}{84} = 6 \frac{1}{4}$