Okay, here we have this:
Let's take John's earnings as x and James's earnings as y, so we obtain the following:
x=y*1.25 (John earns 25% more than James, )
Now, let's clear "y":
y=1x/1.25
y=0.8x
So, finally we obtain that as John's earnings are x and James's earnings are equal to 0.8x, that is 20% less than John's earnings. This mean that the statement is true.
