E.g
Quantity: 12 grams
Relevant property: Conjuring
Target value: +82 +/- 3
Relevant property: Power
Target value: +78 +/- 3

So, you get 3g Bumroot, 3g Leafy Slorgblossom and 3g Bagguss Pulp. You carry out an action and get 80Conjuring,78 Conjuring and 90Conjuring respectively.

When combining, [(3x80) + (3x78) and (3x90)]/12=62. Then, pick out an ingredient and work on it till you get conjuring 82 +/- 3. Hope it help with those who are still lost with combination.

If the composite require 4 ingredients, I work on 3 first, then take out another ingredient to get the final value.

I'm only at Level 4, hope this helps!