Sometimes a certain value of resistance is not available from the values normally available.  Assume that you need a 23 kW resistor.  You have available a supply of 10, 22, 27 and 47 kW resistors.  You can connect them in any sort of combination you deem necessary. Some combinations are shown below
 
 

A.	.B.	C.
D.	E.	F.
G.	H.

• Using your new-found expert knowledge find the equivalent resistance of all combinations which consist of "reducible" series or parallel combinations.
• Determine which combination comes closest to 23 kW.
• Can you determine a combination that comes closer than the closest of these?