Well my friend generally speaking, syrian rue(peganum harmala)seeds contain 3%-4% desirable alkaloids. We'll use the number 3% just to be safe. So assuming this extract has ten times less undesirable plant material:
3% / 100% = 0.03 (using the definition of a percent)
0.03 * 10 parts good stuff by weight / 1 part yucky stuff by weight = 0.30
So now to calculate approximately assuming the sellers claim is true the amount of goodies per x grams of extract:
X grams * 0.30 = Good Alkaloids.
For example: 10grams extract * 0.30 = 3 grams of good alkaloids.
Hopefully I didn't beef up the math but that should be correct.
It's been fun. Thanks for all the wisdom.