Reasoning in Probability Questions

[frog0101]

Hi,
For Probability Questions in the HSC, such as 2003 HSC Q4c or 2004 HSC Q5b, are marks given for reasoning? For each probabilty question, should we give reasoning as this could lead to potential marks even if our answer is incorrect? How much reasoning is required if any, or are diagrams better?

2003 HSC:
http://educationstandards.nsw.edu.au/wps/wcm/connect/dede688e-11d3-4752-b40d-b83e42941906/maths-ext2-hsc-exam-2003.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-dede688e-11d3-4752-b40d-b83e42941906-lGd8Xdw

2004 HSC:
http://www.k6.boardofstudies.nsw.edu.au/wps/wcm/connect/c03be093-eab2-405b-9de4-b2f9986e3f96/maths-ext2-hsc-exam-2004.pdf?MOD=AJPERES&CACHEID=ROOTWORKSPACE-c03be093-eab2-405b-9de4-b2f9986e3f96-lGd7Z3z

Thanks

[RuiAce]

You should give enough reasoning so that the examiners understand your idea behind solving the question. Because if you explain to them what you tried to do, then even if your numbers/expressions aren't correct they'll know that you've tried to work in the right direction, which will give you 1/2 of the marks.

Incidentally, both of these questions were best approached by use of the complement. Recognising how to use the complement would probably have been sufficient for the first mark.

(Diagrams can be both better or worse. If your diagram clearly communicates what's going on, brilliant. If not, well who knows.)