00:01
Okay, so for this problem, we have two resistors r1 and r2 that are in series.
00:06
We'll sum together to be total resistance of 690 and these same two resistors, but in parallel, we'll add together to be a total or equivalent resistance of 150.
00:17
So right here, this and this are your two equations, and so all you need to do is solve for one of them, plug it into the other, and go through the algebra.
00:27
So for me, i think the easiest is i'm going to take this.
00:30
This parallel equation here, multiply everything by r1, r2.
00:34
So that gives us r2 plus r1 equals r1 r2 over 150.
00:43
Notice that r1, r2 added together is 690, so i'm going to replace this right here with 690 equals r1, r2 over 150, and i'll just solve this for r1.
01:01
Is going to be equal to 690 times 150 divided by r2, which that's good.
01:11
Full number here is 103 ,500 over r2...