Thanks all for your enlightening answers.
Indeed I'm learning as I teach, perhaps levels in this could be discussed. I'm in awe of the knowledge on this forum (some times...).
I'm getting a pretty good idea of what this is about. The question about mixing the bypassed air with the core air is brought up in the "exhaust" chapter where I teach the method of external mixing and internal mixing.
Would it be true to say that the 737 NG (with CFM engines) has external mixing? I would still claim this to be a high bypass engine, even though the outer cowling does not reach beyond the aft part of the engine core (which in turn goes one step to it being an unducted fan and then on to a propeller and so on...)
The typical Airbus with RR engines (two spool I believe?) I've understood uses internal mixing? The only difference from my point of view is that the outer cowling reaches further aft than its CFM counterpart and allows bypass air and core air to mix before exiting rearwards.
Both have fans, both have a bypass ratio, but the method of mixing differs.
/LnS