I'll try to simplify the concepts:
Always use the int'l units of measure (kg and liters). If you're using mL, then you should be using grams.
Q: How many miligrams of Lido are found in 40 mL of a 1% solution?
A: 0.4 grams
1% solution => 1 gram of Lido for every 100 mL of solution.
Q: A pt has an order for 200 mL of a 2% Lido solution. How many mgs of lido are contained in this order?
A: 4000 mgs.
2% solution => 2 gms for each 100 mL => 4 gms for 200 mL.
The problems asks for mgs. 4 gms = 4000 mgs.
Q: You have 2 mL of Epi 1:10,000. How many miligrams of Epi are contained in this solution?
A: 0.2 mgs.
1:10000 = there's 1 gram of epi for each 10,000 mL of solution.
In 2 mL you'll have 2/10,000 grams, or 0.0002 grams.
The problem asks for miligrams, so you multiply the grams by 1,000.
Any more questions, give me a holler. I'm an ex-engineer...
Look on the web for more problems.
I say I have to make no mistakes with such problems, at 2:00 am, after 5 beers... that's how important I think it is. A digit mistake means serious complications with my patient.