Reconstitution math

Help, my school hasn't explained these yet since we don't actually get trained in IVs for 3 more months but the questions are in our ATI testing. Here's a sample question on a practice test... How do you calculate this problem??

order reads solu medrol 100 mg IV q 6 hr. Label reads 500 mg of powedered solu medrol for IM or IV injection. Label states "reconstitute with 8 ml of bacteriostatic water." after reconstituting the solu medrol how many mg/ml of solu medrol are there? ____mg/mL

followup question states: to adminster 100 mg, the nurse draws up how many ml from the medication vial to adminster the ordered 100 mg? ____mL

Haven't done reconstitution yet, either, but wouldn't it be 500mg/8ml = 62.5mg/ml? Then for 100mg, divide by 62.5mg/ml and get 1.6ml? Did this without a calculator in front of me and without having done it yet in class, but seems reasonable, no? Could be wrong, usually am, just thought I'd give it a shot! Hope you get it! :)

Haven't done reconstitution yet, either, but wouldn't it be 500mg/8ml = 62.5mg/ml? Then for 100mg, divide by 62.5mg/ml and get 1.6ml? Did this without a calculator in front of me and without having done it yet in class, but seems reasonable, no? Could be wrong, usually am, just thought I'd give it a shot! Hope you get it! :)

This is correct although you can always use this formula...

What you want to give/what you have times mL/tab amounts, so for this question it would be 100mg/500mg x 8mL = 8/5 or 1.6mL