1. figuring out original gravity given x amount of dilution: for example i have 3 gallons of wort @ 1.080 and i want to know what the gravity will drop to with each gallon of water i add to it.

2. my goal here is to brew a concentrated wort and then dilute it into two different strength batches: so if someone could tell me how to calculate the following:

say i have 3 gallons of 1.080 wort and i want to split that into two batches, say one batch of 1.040 and one batch of 1.050 and lets assume that i split the original 3 gallons in half, so 1.5 gallons in each carboy. Then all i need to know is how much water to dilute each carboy with in order to achieve the desired strengths.

Sorry if this is complicated, i know it is possible, probably basic high school algebra, but i am retarded. thanks