hey....look.............

the middle wire has resistance 10 ohm..............

the slant heights of       A          below the middle pont has 10 and 10 ohm

 

right...............

and the slant height above it has resistance 10 ohm...............ok.

 

mow we have to calculate across the ends ...right................

now    the middle wire and slant heights each of resistance 10 ohm are in parallel...................................

theredore 20 and 10 ohm are in parallel................ok

then resistance become = 20/3

now slant heights below of 10 ohm each and 20/3 are in series

 

therefore

 

equivalent resistance =80/3 ohm

 

i m not sure ..................

but i think it is right

tahnku