I have an older version of the IREX book so this may have changed or I could be interpereting it wrong.

The question asks for the minimum height at which a decision to continue or commence a missed approach is to be made in an aircraft without PEC.

The DA for ILS RWY 01 at Brisbane is 220 (208-0.8)

Without PEC, the decision altitude would be 220 + 50 = 270ft. This is the answer given in the book.
So this would mean the decision height would be 208 + 50 = 258ft?
Or is decision altitude and decision height interchangable and both terms reference the AMSL value?

Also in the revision set 5 answers, (again this may have been changed or I'm reading it wrong) the answer to question 11 reads "The obstacle clearance criteria for old and new charts differs. For old criteria charts it is 400 ft for all aircraft. For old criteria charts it varies with aircraft category..." I think it is meant to say for new criteria charts it varies with aircraft category.

I have checked the errata and couldn't find anything.

The term 'height' when used alone is the vertical distance from a specified datum [See AIP GEN 2.2 - definitions].

Therefore the minimum height at which the decision is made could refer an altitude or a height above ground level. The question was never meant to be mean and tricky, so I'll have a look at it and decide whether to change the wording to avoid confusion.