42/50 expressed as a percentage is 84.00%. This simple conversion shows that the fraction is just a little under a whole, and the rounded percentage makes it easy to read.
When you write 42/50 as a decimal, it becomes 0.84, which is the same as 84 out of 100. Seeing the number as a percent helps when you compare it to other values that are already in percent form.
In everyday situations, you might use this percentage to describe a score, a discount, or any proportion where 50 parts represent the whole. Knowing that 42 out of 50 equals 84.00% lets you quickly understand the size of the part compared to the total.