Simple Error Could use some help

[xpack]

http://img401.imageshack.us/img401/3074/38927294.png I added r1 and r2 together to produce 8.571 and made
I=10/8.571
and
I'=10/8.671
and subtracted I from I' and got .013
But my teacher marked the answer as .004

How is this?

 

[berkeman]

http://img401.imageshack.us/img401/3074/38927294.png


I added r1 and r2 together to produce 8.571 and made
I=10/8.571
and
I'=10/8.671
and subtracted I from I' and got .013
But my teacher marked the answer as .004

How is this?

I believe R2 is irrelevant to this question.

The delta-I comes about because in one case you have 10V across R1, and in the other case, you have 10V across <what?>...

 

[xpack]

Oh okay thanks, that's what I thought but I didn't think the teacher would put an r2 if it wasn't relevant guess I was wrong.

 

[berkeman]

Oh okay thanks, that's what I thought but I didn't think the teacher would put an r2 if it wasn't relevant guess I was wrong.

Yes, it's a little sneaky, but it helped to teach you something extra on this problem, so it's worthwhile.