55:90

If you mean the ratio 55:90:

• Simplest form: 11:18 (divide both by gcd 5)
• As a fraction: 11/18 ≈ 0.6111
• As a percentage of 90: 55 is 61.11% of 90
• If you view the total (55 + 90 = 145): 55 is 55/145 ≈ 37.93% of the total, and 90 is 62.07%.

If you had a different interpretation in mind, let me know.