4per5 + 1per2×6per15

[tex] \frac{4}{5}+ \frac{1}{2}\times \frac{6}{15}\\ =\frac{4}{5}+ (\frac{1}{2}\times \frac{2}{5})\\ =\frac{4}{5}+ \frac{1\times2}{2\times5}\\ =\frac{4}{5}+ \frac{1}{5}\\ = \frac{5}{5}\\ \bold{=1} [/tex]