Since this is out of 4, you can think of 4 as being 1. Now each part of 4 needs to have an equal value so you need to split 1 into 4 equal values. So half of 1 is 0.5 and half of 0.5 is 0.25. So, each part of 4 has a value of 0.25.
1/4 = 0.25
2/4 = 0.50
3/4 = 0.75