[eschwartz]

Try this. Sorry it's a little bulky, I have tried to comment the more obtuse bits.

program:

# if either is empty, return zero for reviews
r = test(
	field('#chapters'),
	ifempty(
		field('#reviews'),
		'0'
	),
	'0'
);
# don't divide by zero.
c = ifempty(
	field('#chapters'),
	'1'
);

ans = divide(r,c); 

cmp(
	ans,
	0,
# if zero return blank
	'',
	'',
	ans
)