question about % solutions

Here's the problem:

Order: Calcium Gluconate 500mg IV

Available: Calcium Gluconate 20% Solution

so, does 20% mean 20g per mL? Assuming that it does, this is how I worked out this problem:

500mg = 0.5g

20% = .2

50/2 = 2.5mL

so D/H * V = A

D=0.5g

H=.2

V= 1mL

A= 2.5 mL

Is this correct? There are only two problems involving % on my practice sheets and I couldn't find any in our book. A classmate says 20% means 20g per 100 mL, but the problem doesn't work out that way.

Here's the other % that I did:

Order: Calcium Gluconate 0.25g

Available: Calcium Gluconate 10% =0.1

2.5/1 * mL = 2.5 mL

I know, they both have the same answer, but according to my answer key, this is correct.

So am I right in thinking that 20% means 20g per mL? When dealing with % solutions, will they always be in mg or g?

Thanks!