2.5g order 50mg/ml on hand how many ml's do you need to give the ordered amount?

Get a ruler in your hands. Measure things until you start to understand how a ruler works. Measure some stuff and figure out where the center is. Say you measure a book and it's 7/8" thick. You look at your ruler and see that every eighth is divided into two sixteenths, so obviously half of 7/8" is going to be 7/16". If you write that out you have 1/2 x 7/8 = 7/16. And you notice that 1/2 is divided into 2/4 and then into 4/8 and so on, so you can convert anything to anything by multiplying all the numbers on top and then all the numbers on bottom.

Other rulers are divided into 10 and 100 parts. But an inch is still an inch, so anything on one ruler can be translated to the other ruler. A half inch on one ruler is 5/10 or 50/100 on the other. An eighth inch is just 12.5 marks when you have 100 marks per inch. A metric ruler divides an inch into 25.4 parts, so a half inch would be 12.7 of those parts. Pretty simple, isn't it? Practice this a bit and people will think you went to wizard school.

"2.5g order 50mg/ml on hand" So you have a ruler marked in g and another one marked in mg and you know it takes 1000 mg to equal a g. You can change that to 0.05 g or you can change the other one to 2500 mg. You do this in your head unless you are working double shifts and are half asleep. 2500 over 50 is the same as 250/5 and that reduces to 50 so the answer is 50 ml.