How do I find the equivalent resistance

Determine the equivalent resistance seen between points a and b when R1 = 2.7 , R2 = 3.4 , R3 = 9 , R4 = 39.7 , R5 = 3.4 , R6 = 5.2 , R7 = 0.3 , R8 = 5.5 , R9 = 14.9 , and R10 = 15.6 .

I know the answer is 11.9 ohms. I just don't know how to get there.

Here's the circuit diagram: http://imgur.com/1k4CO.jpg

R3 + R8 => series R38 = 9 + 5.5 = 14.5
R38 || R10 => parallel R38_10 = 1/(1/14.5 + 1/15.6)) = 7.52

R38_10 + R4 => series R38_10_4 = 7.52 + 39.7 = 47.22

similarly,

R5 + R2 => series R52 = 3.4 + 3.4 = 6.8
R52 || R9 => parallel R38_9 = 1/(1/6.8 + 1/14.9)) = 4.673
R52_9 + R1 => series R52_9_1 = 6.8 + 4.673 = 7.373

R38_10_4 || R52_9_1 => parallel Rt = 1/ (1/47.22 + 1/7.373) = 6.8

R =Rt + R6 + R7 = 6.8 + 5.2 + 0.3 = 12.3

A little bit over..., check the calculations... I don't have a scientific calculator handy (using a regular one now). But this is the concept. Hope this shows...

Add series elements to combine them.
Then combine parallel elements to combine them.
Keep going until done.