Bonjour,
[tex] \frac{45}{63} \div \frac{72}{28} + \frac{13}{18} = \frac{5}{7} \div \frac{18}{7} + \frac{13}{18} = \frac{5}{7} \times \frac{7}{18} + \frac{13}{18} = \frac{5}{18} + \frac{13}{18} = \frac{18}{18} = 1[/tex]
[tex] \frac{9 \times 10^{4} \times 2 \times {10}^{ - 8} \times 2 \times {10}^{3} }{2 \times {10}^{ - 7} \times {10}^{4} } = \frac{9 \times 2 \times {10}^{ - 1} }{ {10}^{ - 3} } = 18 \times {10}^{2} [/tex]
