[tex]\text{What percent of 80 is 90?}\\\\\text{Calculate what fraction of the number 90 is 80}\\\\\dfrac{80}{90}=\dfrac{8}{9}\\\\\text{Convert it to percent}\\\\\dfrac{8}{9}\cdot100\%=\dfrac{800}{9}\%=88\dfrac{8}{9}\%\\\\Answer:\ \boxed{80\ is\ 88\dfrac{8}{9}\%\ of\ 90}[/tex]