If i need to dilute 50% dextrose into 20mg of a 2.5% solution, how would i do that?

First, convert your %solution into a Molarity: [(%solution)*10]/FW

This answer gets you g/L

Since Dextrose (or d-glucose) is C6H12O6, it has a formula weight (FW) of 180.16 using your periodic table.

= 0.02775M (keep the sig digits for now)

Do the same for a 2.5% solution: you get 0.00139M

Finally, convert 20mg to of 0.00139M C6H12O6 into liters, and use your friend M1V1 = M2V2 (M is molarity and V is volume).

I am three years removed from all this, so double check your and my work. I am assuming this "explanation" is better nothing. Especially check units, and that is always.