I knew of the Concrete Mathematics text from way back, “a blend of CONtinuous and disCRETE mathematics” as the authors put it. It’s very interesting material, though I was a little surprised to see it taught at a HS and wondering if this referred to something else.
In many ways it does make sense to study them together. Continuous math often has its parallels in discrete math, and vice versa.
Note: Edited by yikesyikesyikes to avoid doxxing the OP.