What is 21 out of 27 is

7/9 or 0.777777

21/27=.7777
if you want it in percent times it by 100
and you get 77.7% or if you want to round up 78%
3(7)/3(9) if you want to put it in lowest form
7/9 the 3 is there to show you that 3 is the number you divide by to get 7 and 9

Reduce to lowest terms by dividing by 3.

7/9 = 0.77777

I hope this information was very helpful.

21/27 reduces to 7/9.

21/27

Try google or a calculator

21/27 = 3(7)/3(9) = 7/9