Let the cost be c, and the normal mark-up x, then the bormal price is:

P = c(1+x)

discounting this by 25% means the store sells for:

D = 0.75 P

which is a gross profit of 25%, so:

D = 1.25 c

so we have:

0.75 c (1+x) = 1.25 c

which after cancelling the c and rearranging gives:

(1+x) = 1.25/0.75 ~= 1.667,

so th normal markup is ~=0.667 of 66.7%.

RonL