Question

13.Calculate the total effective resistance between points A and B

Answer 1

HEY MATE...
HERE'S THE ANSWER
___________

3ohm and 3 ohm are in series
so according to formula
R=R1+R2
3+3=6 ohm
similarly
3+3=6 ohm

Now 6 ohm and 6 ohm are in parallel
so
according to formula
1/R=1/6+1/6
1/R=2/6
1/R=1/3
then
R=3ohm...ans

Answer 2

I gave names to the four ressistors - P,Q,T,and S.... [ The red lines indicates RESISTORS ]

Effective resistance of P and Q ... it is a series

$R_{pq} = 3 + 3 = 6 \: ohm$
and effective resistance of S and T is also 6 ohm

Total effective resistance between A and B .... Rpq and Rst are parallel...so ...

$R_{ab} = \frac{1}{ R_{pq} } + \frac{1}{ R_{st} } = \frac{1}{6} + \frac{1}{6} = \frac{2 }{6} = \frac{1}{3} \\ \\ R_{ab} = 3 \: ohm$