Ms. Fried says: "The first thing I do with my students is to teach
them the difference between the OT and the HB.
I tell them the OT is the LXX!
(Not one of them has ever argued with me about it!) :)"
The way you define the Old Testament is close to true (but not quite) for
Roman Catholics and Eastern Orthodox Christians, but is definitely not
true for Protestant Christians. The LXX includes the Apocrypha, which
Protestants reject from being part of their Old Testament. Moreover,
virtually all modern translations of the Old Testament by Christians of
whatever stripe are based first and foremost on the Masoretic Text of the
Hebrew Bible, not the LXX. Though the latter is regularly utilized for
text-critical purposes, the Hebrew Bible is the main text.
The fact none of your students have ever argued with you reflects their
ignorance, not the correctness of your assertion. It reminds me of
someone's definition of a lecture: A lecture is when ideas go from the
notes of the professor into the notes of the students without passing
through the minds of either one.