Question

How do you write 18/20 a percentage

Answer 1

$\frac{p}{100}=p\% \\ \\ \frac{18}{20}=\frac{18 \times 5}{20 \times 5}=\frac{90}{100}=90\%$

18/20 is equal to 90%.

Answer 2

When you say "Percentage", it means automatically that it's a number/100 
here you have 18/20, to make the percentage, you need to make it /100 
100/20 = 5
so you need to multiply the the numerator and denominator of 18/20 by 5, which gives you 90/100, which means 90%
Hope this Helps :)