# 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
4 years, 11 months ago

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Sounds like a potentially good puzzler. Although, what a subpart is, isn't clear.

- 4 years, 11 months ago

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.......

- 4 years, 11 months ago

What is a technothlon?

- 4 years, 11 months ago

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

- 4 years, 11 months ago

Oh. Thanks for the link

- 4 years, 11 months ago

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.....

- 4 years, 11 months ago

From classes 9th to 12th

- 4 years, 11 months ago

Its answer is 8

- 4 years, 11 months ago

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

- 4 years, 11 months ago

Probably 10

- 4 years, 11 months ago