Find the least number lying in -100 to 100 exclusive to be subtracted from 200 to make it a perfect cube.
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This solution actually hides the "proper" way to approach the question. Instead of suggesting that "perfect cube nearest to 200 are 216, 125", it should instead be phrased as "We are interested in the region 1 0 0 , 3 0 0 , and the only perfect cubes here are 125 and 216. Thus, the smallest is 2 0 0 − 2 1 6 = − 1 6 ".
While Sandeep did essentially say all of that eventually, the phrasing and ordering of the solution made the crux of it much more obscure.
Let me see how many of Brilliant guys are trapped in my trick. :P
Upvote this comment if you got trapped.
Thanks !
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But I am not trapped.
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then you can upvote the solution. :P
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@Sandeep Bhardwaj – I will surely do it
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@Rama Devi – Thank you ⌣ ¨ for you kind Job. :P
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@Sandeep Bhardwaj – Then why don't you try my new set - Logic ?
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@Rama Devi – I'll try surely.
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@Sandeep Bhardwaj – Try to be in the top of the leader board.
Oh come on!!!Guess I'm the first to be caught in your net eh?Nice trap btw sir Sandeep!
Sandeep sir i am preparing for RMO and also an aspirant for IIT-JEE. So, will you please suggest me some good books for especially maths and physics.......
Objection! λ = − 1 4 3 gives 2 0 0 − λ = 7 3 , and − 1 4 3 < − 1 6 . And so on for 8 3 , 9 3 ... Hence no such number exists.
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Ohhh!! Thank you for pointing it out. I forgot to use that condition. Now I mentioned that. Sorry for the inconvenience caused !
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Great! Remember, don't stop breaking after the first glass ;)
The answer is -16 , which when subtracted from 200 , gives the answer as 216 , which is the nearest perfect cube to 200.
Why? Where's your working?
Let n be the integer − 1 0 0 < n < 1 0 0 and m = 2 0 0 − n .
Therefore, the smallest n m i n = n 2 = − 1 6
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Let λ be the least no. to be subtracted from 2 0 0 to make it a perfect cube.
∴
2 0 0 − λ = a 3
Perfect cube numbers nearest neighbors to 2 0 0 are 2 1 6 , 1 2 5 .
case 1 :
Let a 3 be 1 2 5 for which value of a will be 5 .
⟹ 2 0 0 − λ = 1 2 5
⟹ λ = 7 5
case 2 :
Let a 3 be 2 1 6 for which value of a will be 6 .
⟹ 2 0 0 − λ = 2 1 6
⟹ λ = − 1 6
∙
If you take any other case than the above two, the value goes out of the range
( − 1 0 0 , 1 0 0 )Out of the above two values of
λthe least value is
− 1 6 . (which is not given in the options)So, the correct option is None of the given.
enjoy !