I'm not sure why you're saying this is not true. Can you explain why?
Continuing...
If 3/4 - 2/3 = 100 l.
then 1/12 = 100 l.
and tank capacity is 1200 l.
Hi:
The difference between a tank that is 3/4 full and a tank that is 2/3 full is 100 litres. The word "difference" implies 'subtract'. So if (3/4 - 2/3) = 100l, what is the volume of the whole tank?