BapraHT 2 (3)/(5)cdot (25)/(4) (15)/(4):(3)/(7) (1)/(frac (1)(21)+(1)/(28)) 6cdot ((1)/(3))^2-17cdot (1)/(3) 6,9+7,4 8,9cdot 4,3 (9,2)/(0,5-2,8)

1. $\frac {3}{5}\cdot \frac {25}{4} = \frac {3 \cdot 25}{5 \cdot 4} = \frac {75}{20} = \frac {15}{4}$<br />2. $\frac {15:\frac {3}{7} = \frac {15}{4} \cdot \frac {7}{3} = \frac {15 \cdot 7}{4 \cdot 3} = \frac {105}{12} = \frac {35}{4}$<br />3. $\frac {1}{\frac {1}{21}+\frac {1}{28}} = \frac {1}{\frac {4}+\frac {3}{84}} = \frac {1}{\frac {7}{84}} = \frac {84}{7} = 12$<br />4. $6\cdot (\frac {1}{3})^{2}-17\cdot \frac {1}{3} = 6 \cdot \frac {1}{9} - \frac {17}{3} = \frac {6}{9} - \17}{3} = \frac {2}{3} - \frac {17}{3} = -\frac {15}{3} = -5$<br />5. $6,9+7,4 = 14,3$<br />6. $8,9\cdot 4,3 = 38,37$<br />7. $\frac {9,2}{0,5-2,8} = \frac {9,-2,3} = -4$