Question

If the total resistance in a parallel circuit is 750 ohm’s and R1 = 3000 ohm’s and R2 = 3000 how do you find R3?

Answer 1

do it with conductivity (inverse of resistance)(adds in parallel)
c = 1/750 = 1/3000 + 1/3000 + 1/R3
1/750 = 2/3000 + 1/R3
1/R3 = 1/750 - 2/3000 = 4/3000 - 2/3000 = 2/3000
so
R3 = 3000/2 = 1500