Question

Show how would you connect 3 resistors each of resistance 3Ω so that the total resistance is
1:-9Ω
2:-1Ω
3:-2Ω

Answer 1

Solution :
             Case1 :
                        Sum of resistance =9Ω
                 Connect three resistors of resistance 3Ω in series , the resultant resistance will be 9Ω.
      Case 2 :
                 Resistance = 1Ω
         Connect three resistors of 3Ω in Parallels , the resultant resistance will be 1Ω.
Note : when we connect n resistors of equal resistance (R)in parallels , the equivalent resistance is given by Resistance of Resistor/total number of resistors. 
here in above case equivalent resistance will be 3/3 = 1Ω
Case 3:
          Resultant Resistance = 2Ω
     This case is not possible by using three resistors of 3Ω resistance each.

Hope this helps you.

Note : when resistors are connected in Series their resistances add up.

Answer 2

how would you connect 3 resistors each of resistance 3Ω so that the total resistance is1:-9Ω
2:-1Ω
3:-2Ω

Solutions 

1) Sum of resistance =9Ω
 Connect all three resistors of resistance 3Ω in series , the resultant resistance will be 9Ω.

2) Resistance = 1Ω
Connect all three resistors of 3Ω in Parallels , the resultant resistance will be 1Ω.

Remember : -- when you connect n resistors of equal resistance (R)in parallels, the equivalent resistance is given by Resistance of Resistor/total number of resistors. 
Equivalent resistance will be 3/3 = 1Ω

3) Resultant Resistance = 2Ω
 This case is not possible by using three resistors of 3Ω resistance each.

when resistors are connected in parallels their resistances always add up.