Question

how can three resistors of resistance 2 ohm 3 ohm and 6 ohm be connected to give a total resistance of 4 ohm and 1 Ohm

Answer 1

for 1 Ω they will be connected as parallel combination 

Answer 2

connect all the resistance in parallel then you will get effective Resistance of 1 ohm.
for effective Resistance of 4 ohm connect 2ohm and 6 ohm resistance in parallel and 3ohm in series.

hope it helps