he,he you fall for it...
the problem is this:it's not a mathematical question,it's physical one.
If you study the water phase diagram ,the tripple point is 273.15K.
It is a unique temperature value,not some math figures. This is 0 C. This value can not be multiplied,physically speaking.It's like you'll try to divide by 0 in maths.
The only value used in calculations regarding temperature modifications is the Delta T.
20C is 273+20 K
Duble than this is 273 +(20*2)=313 K= 40C
The answer that we've expected.
It's normal physics.
We should not multiply the origin,only the deltaT.I'll give you another example:
suppose today I walk 10m from A to B.Tomorrow I'll walk another 10m,so double distance from the start.
Now suppose point A is 100m from the origin X.
The distance that I've walked in the first day is 10m or 110m? See my point? Then the double is 20m or 220m? If it's 220m,then by deducting 100m you'll find the value in the first scale used? WRONG. (compare to the Oddone example)
That's it.You should not multiply the origin ,and also changing scales used during calculations can be very tricky for inexperienced people.
Brgds...
Alex