42.50% is what you get when you turn the fraction 34/80 into a percentage.
The fraction 34/80 can be simplified to 17/40, which still represents the same part of a whole. Whether you write it as 34/80, 17/40, or 42.50%, the value stays the same.
In everyday use, the percentage form is often the easiest to understand. If you see 42.50% on a chart or a label, you know it means the same amount as the original fraction.
