125apples were shared between jerry and kay. kay received 20% less than jerry.

If that is the case, then Jerry got 60% and Kay received 40%, because together they make the 100%, or in equations:
kay + jerry = 100%
kay = jerry - 20%
substitute:
jerry - 20% + jerry = 100%
2*jerry = 120%
jerry = 60%
kay = jerry - 20% = 60% - 20%
kay = 40%
if you want to know the amount of apples each has:
kay = 40%(125) = 0.4(125)
jerry = 60%(125) = 0.6(125)