For the trial period on her new job Windy has 20% less salary than she had on her old job. By what percent should her salary increase after the trial period to match her old salary?

Her new salary would have to increase by 125% to match her old salary.

Let x be her old salary. Then her new salary is given by 0.8x. We want it to equal 1x, her old salary. To find what we multiply that by (the percent), we divide 1 by 0.8:

1 / (0.8) = 1.25

This is 125%.