There were 90 pizzas and every guest ate 1/6 of a pizza, so the number of guests is:
[tex]\frac{90}{\frac{1}{6}}[/tex]now, let's solve this
Apply the fraction rule and solve
[tex]\frac{a}{\frac{b}{c}}=\frac{a\cdot\:c}{b}[/tex][tex]=\frac{90\cdot\:6}{1}[/tex][tex]=540[/tex]Therefore, the number of guests is 540