51/55 as a percentage is 92.73%. This fraction is close to a whole, so the percentage is high. It tells you that 51 out of every 55 parts are present.
The fraction 51/55 can be useful when you compare parts of a whole, like scoring 51 points out of a possible 55. Seeing it as 92.73% makes it easier to understand at a glance.
In everyday language, you might say something is "about 93%" instead of giving the exact fraction. The rounded value still reflects the same high proportion.
Remember that 92.73% means almost the entire amount, which is why 51/55 is often seen as a strong performance or a nearly complete set.