Typical values for AvGas specific gravity vs temperature are as follows.
Temp ◦C, S.G.
10 , .712
15 , .707
20 , .701
25 , .695
30 , .69
35 , .684
40 , .678
Due to manufacturing tolerances, additives and time of year, there will always be variations from the typical values.
Talk to your local refueller, not only does he have an actual S.G. for each batch of avgas, he also has a whiz wheel for computing the S.G.
Under ISA conditions (15 degrees C) the typical value is .707
The figure of .72 has a safety fudge factor and is not indicative of the S.G. as supplied by the fuel supplier.
Baswell is correct regarding volume, at higher temperatures the volume of fuel is less.
TAA / QANTAS used to take advantage of this fact to enable extra fuel to be loaded.
For a Sydney - Perth flight, originating from Melbourne, the technique was to cruise as high as possible MEL - SYD,
then refuel as soon as possible after landing SYD while the wings / fuel tanks were still chilled.
Racing cars use a similar method, refuelling from chilled containers to get more fuel (volume) into the fuel tank.
As for exams, unless specified, stick to .72, whether its right or wrong, its what is expected.
and finally, a repeat of earlier, for the actual S.G. ask the refueller what was the S.G. when he did his daily dips and tests.