A cool easy problem 7

Electricity and Magnetism Level 3

There are 4 resisters of 12 ohm each .
Which of these resistance is not possible with their combination in series or parallel ?

24 ohm 9 ohm 16 ohm 30 ohm 12 ohm

2 solutions

A Former Brilliant Member
Jan 9, 2015

here we can easily see that only 24 is not a possible combination

how can a combination of 30 be possible with 4 resistors of 4 ohm each...??

sakshi taparia - 6 years, 5 months ago

hey ,
please check
there are 4 resistors of 12 ohm each
I fixed the question

A Former Brilliant Member - 6 years, 5 months ago

oh, ok.... Now its fine

sakshi taparia - 6 years, 4 months ago

you can get 24 ohm by two 12 ohm in series and don't use the other two simply or put them in open circuit in parallel but how you can get 9 ohm???

Mahmod Abass - 5 years, 8 months ago

You can get 9 $\Omega$ by keeping 3 resistors in series and then put that equivalent in parallel with remaining 12 $\Omega$ .

Akhil Bansal - 5 years, 8 months ago

That's right i have figured that out but you didn't answered the main question you can get 24 ohm easily using two 12 ohm in series only or two in series with 2 12 ohmin parallel as open circuit if you want to use all the resistor

Mahmod Abass - 5 years, 8 months ago

@Mahmod Abass – It's understood that if we are provided with 4 resistors and asking about combination of them,we can't simply neglect any 2 or putting them in open circuit(which is same as not using them) .You have to use all the given resistors to reach any conclusion.

Akhil Bansal - 5 years, 8 months ago

@Akhil Bansal – No 1-) it's well known and logically sensible that when you have number of resistor you don't have to use them all because that what happen in reality that you have number of resistor and you want to make combination of them to get an aimed resistance , 2-)if you want problem like that you have to strictly mention that ,man just don't deny that problem has high ambiguity , in any problem you don't read the problem maker's mind you read the problem statement with common logic not his mind logic :)

Mahmod Abass - 5 years, 8 months ago

@Mahmod Abass – Ya,I think it should be mentioned in question that we can't neglect any resistor.

Akhil Bansal - 5 years, 8 months ago

Geoff Pilling
Jun 3, 2016

You might want to specify that you need to use all four resistors....

A cool easy problem 7

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