You don't. Milligrams are a measure of mass, teaspoons are a measure of volume. The two cannot be converted directly into each other. Perhaps if you knew the density of a specific substance, you could figure out how much a teaspoon of it would contain.
3 milligrams is SO small I don't believe you could measure it without lab. equipment. A teaspoon is 5,000 mg, so you can possibly imagine how small 3 mg is.
Depends on the solution or substance. You could have a solution that is mixed at 15mg per 1 ml but if a person needed a more dilute solution then you would mix it with a solvent to make it down to whatever is desired. If you have a metal that is maybe 1gram per cubic centimeter then it would be 1000mg per ml of pure metal
It depends on the density of whatever it is you are measuring. g is a measurement of weight. ml is a measurement of volume. If it's water, then 1g is precisely 1ml.... so 250g = 250ml. If it's something less dense then it could be way more or less.
It could refer to density, where the mass is measured in milligrams and the volume in decilitres. Or It could refer to concentration in a fluid where the mass of the "active" substance is measured in milligrams and the volume of the solution (possibly solute) is measured in decilitres.
You could measure any liquid in milliltres.
No, it could not.
Milligram (mg) is a unit of mass whereas millilitre (mL) is a unit of volume. It's not possible to directly convert between the two without knowing the density of the substance you are hoping to convert. One mL of space may have 19 mg of mass in it, if it's full of gold. But it could also be empty and have no mass in it at all. One gram (1,000 milligrams) is the mass of one milliliter of water at 4°C at sea level.
There are three teaspoons to one tablespoon.1 tablespoon = 3 teaspoons. To convert a value in tablespoons to teaspoons, multiply by 3.
No, but you could get very sick.
I'm not a veternarian, but I will tell you any time that you are administering medication math is a good thing to know. You will need to be able to convert different types of measurement. Milliliters, cubic centemeters, milligrams, grams. A bad dosage conversion could kill an animal.
According to http://www.cag.uconn.edu/NUTSCI/NUTSCI/outrch/pdf/HowMuchSaltSugar.pdf there is 2,000 milligrams of salt in one teaspoon of salt. Using algebra you can determine that there is .36 teaspoons in 720 milligrams of salt.Add 1/4 tsp of salt almost 1/8 tsp of salt together. You could add the full 1/8 tsp of salt but you will have just a little bit more salt than you need. It's not a big difference.