s_pugh, I apologise for the consternation caused by my earlier post. The problem for me is that the riddle in the literary text is ambiguously worded regarding the status of the extra two in relation to the whole. The version of the riddle posed by the Hindu mathematician, Bhaskara II, and elsewhere, is far clearer in this respect.
There is no doubt about the answer to the riddle, which is 72 if fractions are not allowed. For anyone interested, this page deals with the maths:
http://euclid.trentu.ca/math/sb/1101Y/2012-2013/MATH1101Y-Quiz-Solutions.pdf
I very rarely find anything to criticise in Sabre, but in this case I think the theme could have been better implemented.