For the combination of resistors shown in Fig. find the equivalent resistance between the points
C and D

Explanation

Between the points C and D: The resistors `R_2, R_3` and `R_4` are in series. They can be replaced by an equivalent resistance `R_s`, where
`R_s = R_2 + R_3 + R_4 = 3 + 3 + 3 = 9 Omega `.
The resistance `R_5 (= 3 Omega ) and R_s (= 9 Omega )` are in parallel between the points C and D as shown in Fig.

If the equivalent resistance between C and D in Fig. is `R_p`, then
` (1)/(R_p) = 1/3 + 1/9 or (1)/(R_p) = ( 3+1)/(9) = 4/9`
` or R_p = 9/4 = 2.25 Omega `
Thus the equivalent resistance between C and D is 2.25 `Omega `