About Weaving and zip merging: who yields to whom, and the 300/50-metre rule: which statement is WRONG?
The agreement is that every driver on the through lane lets exactly ONE driver from the obstructed lane go first each time — not two or more in a row.
Use all available room up to the narrowing: adjust speed at 300 m, only actually merge at about 50 m.
When zip merging, you only need to adjust your speed right at the narrowing itself; you can just keep driving as you were for the 300 metres before it.
Because mergers drive more slowly and have more room and overview, it is actually the reverse: mergers let the exiters go first.
Explanation
trap: the early adjustment phase skipped. Book p.155 - already at about 300 metres before the narrowing you adjust your speed to the adjacent traffic; only at about 50 metres do you actually merge