The topic of vitamins and supplements is, unfortunately, complicated. There are two primary problems.
First, many mineral supplements come in different forms, which can have large effects on how well the body absorbs them.
Take magnesium for example. Elemental magnesium is what your body needs, but the many different forms of magnesium you can actually take - oxide, carbonate, malate, citrate, glycinate, etc. - are all absorbed differently. Research studies on magnesium in food and supplements show it is absorbed by the body somewhere in the range of 4 - 50%, so at best you're getting half of what your taking metabolized into your blood stream.
The second issue is the dose. To be effective, most supplements normally have a minimum effective dose. The results of taking a supplement are more akin (not exact) to a step function where once the effective dose is reached "results happen", versus the commonly believed (but usually wrong) idea that if you take 20% of the min effective dose you get a 20% improvement. This is also true for many pharmaceutical drugs as well and one of the things determined in drug trials.
Continuing with the magnesium example, a rule of thumb for magnesium dosage is somewhere in the range of 3 - 4.5mg/lb, or approximately 600-900 mg per day for a 200 lb person. The above multivitamin label only contains 50mg of an unknown type of magnesium, which is typical for most mass market multivitamins sold in the US.