I appreciate these questions every day, helps me learn new things, so I don't want to sound like a nob here, but surely the question is wrong?
'If I have this data?
Working on that, to get it as 1,2,3,4 DENSE_RANK() would not work, as it would be 1,2,3,3.
In the answer, it gives the data as:
( 1, 100), ( 2, 50), (3, 50), (4, 120), (5, 25)
Which would relate to 1,2,3,3,4 as the question asks.
A good one for me to look at from a learning point of view, as I had to look into the data to understand, but at first I was massively confused my answer of row_number was incorrect!