This question is testing INTEGER CONSTRAINTS. If we have $5 bills and $20 bills, we have to have a whole number of each.

With these types of problems in DS, it's useless to set up an equation. 5x + 20y = 125 will look unsolvable, as algebraic equations can't account for integer constraints. Instead, make a CHART:

Start with the maximum # of 20's - it's usually easier to start with the bigger one:


You don't have to fill in everything, but just enough to notice patterns to start. Then, fill in the # of 5's that would add up to $125 total:


Now when you're looking at the statements, here's your goal:
See if the statements restrict it to a single scenario in your chart.

(1) Max has fewer than 5 bills worth $5 each.
Cross off any scenarios in your chart that don't apply:


This leaves us with a single scenario:


That's sufficient!

(2) Max has more than 5 bills worth $20 each.
Do the same thing here: eliminate the scenarios that don't fit.


Once again, there's only one scenario left that fits:


That's also sufficient.

The answer is D.

Here's another example of how to use a chart with integer constraints:
https://www.beatthegmat.com/a-factory-p ... tml#765462