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Inverting Coins

There are 20 coins placed on a table such that tails is showing up. Suddenly electricity goes off and a boy sitting nearby inverts few coins and then he asks another boy to select some coins such that number of inverted coins is equal in every other subpart. He selects 8 coins and invert those 8 coins , and when electricity comes back he sees equal number of inverted coins in both subparts. Tell how many coins did first boy inverted.

P.S. The question is not original.

Note by Ratul Pan
2 months, 3 weeks ago

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If you assume n coins to be inverted in both, then first would have inverted his n and others 8-n. So he inverted 8 in total Prince Loomba · 2 months, 2 weeks ago

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Its answer is 8 Prince Loomba · 2 months, 2 weeks ago

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Sounds like a potentially good puzzler. Although, what a subpart is, isn't clear. Agnishom Chattopadhyay · 2 months, 3 weeks ago

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@Agnishom Chattopadhyay The problem is given in a technothlon problem . I am also confused with the term subparts. But it sounds like two groups from the phrase "equal number of inverted coins in both subparts". The options were given as 5 , 8 , 10 , 12. Now you can try....... Ratul Pan · 2 months, 2 weeks ago

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@Ratul Pan What is a technothlon? Agnishom Chattopadhyay · 2 months, 2 weeks ago

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@Agnishom Chattopadhyay From classes 9th to 12th Prince Loomba · 2 months, 2 weeks ago

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@Agnishom Chattopadhyay It is an exam purely based on logic conducted by IIT Guwahati. You can check it out in the official website i.e. technothlon.techniche.org Ratul Pan · 2 months, 2 weeks ago

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@Ratul Pan Oh. Thanks for the link Agnishom Chattopadhyay · 2 months, 2 weeks ago

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@Agnishom Chattopadhyay Its my pleasure...... You can register now also. The exam is on 17 th of july and I think registrations are open till 13 th of july..... Ratul Pan · 2 months, 2 weeks ago

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Probably 10 Hemanth K · 2 months, 2 weeks ago

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@Hemanth K Read my answer. Its 8 Prince Loomba · 2 months, 2 weeks ago

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