55:2

Do you mean:

• 55 ÷ 2 = 27.5 (or 27 1/2), or
• the ratio 55:2 (which is already simplified; equals 27.5:1 if you normalize to 1 part 2)?

If you meant something else (like 55 choose 2), let me know and I’ll give that too. For reference, 55C2 = 1485.