UGC NET CSE | December 2012 | Part 3 | Question: 29

Question

$58$ lamps are to be connected to a single electric outlet by using an extension board each of which has four outlets. The number of extension boards needed to connect all the light is

• A. $28$
• B. $29$
• C. $20$
• D. $19$

Answer 1

connect First 4 Lamps(L1 , L2 , L3 , L4) to extension 1 and take power from Extension 2 . In Extension 2 we can connect only 3 lamps because out of 4 one port is busy to supply power to extension 1.

Similarly, For other extensions we can connect only 3 lamps because one port is busy to supply power to other extension.

Connect Last Extension (Ex 19) to Electric outlet.

We can connect 4 Lamps to first extension

Number of Extension required for Remaining 54 lamps = $\frac{54}{3}$=18 Extension

Total Extension required to connect all 58 Lamps = 18+ 1 =19

Hence,Option(D)19 is the correct choice.

Comments

ceil(15/4) = 4.

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@papesh if you do like that you are giving some vacant spots in the board. Method by Leen is way better and systematic.

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@PApesh.. Can u please explain ur approach.. I could not understand

Answer 2

All extensions can allow 3 lamps and one plug for next extension. 

Thus,         3)58(19

                     57

                 ---------

                      1

So we have got solution for 57 lamps, but one lamp still needs to be connected. But, this time in the last 19th board, we have one outlet also left..

So, 19 extension boards will be enough.