Realise the problem now thanks Paul

Radar you are correct. The calculations in the 3rd sheet is the correct answer.

What I did not realise the student had done wrong is to treat the whole calculation as entirely parrallel. He correctly worked out the equivalent resistance for each of the three groups of resistors but then he should have treated the rest of the problem as a series circuit.
Then it would have worked out.

Some times you just can not see something obvious when you look to hard... [Linked Image]

der Großvater