Why is the minimum resistance 2.4 ohms with 3 and 12 ohm resistors?

[roxas]

what is the smallest resistance that can be obtained by using onlu a 3 ohm resistor and a 12 ohm resistor??

can anyone please tell me why the answer is 2.4ohm?

i calculATED USING 1/3 = 1/2 AND I GOT 4 OHMS

thx anyway

 

[Hootenanny]

Okay, if the resistors are placed in series the effective resistance of the system is simply the sum of the individual resistances (i.e. $R_{t}=3+12=15\Omega$).

However, if we place the resitors are placed in parallel the effective resistance of the array is...?