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.

#Logic

Easy Math Editor

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`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
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Comments

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

Agnishom Chattopadhyay - 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.......

Ratul Pan - 4 years, 11 months ago

What is a technothlon?

Agnishom Chattopadhyay - 4 years, 11 months ago

@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 - 4 years, 11 months ago

@Ratul Pan – Oh. Thanks for the link

Agnishom Chattopadhyay - 4 years, 11 months ago

@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 - 4 years, 11 months ago

@Agnishom Chattopadhyay – From classes 9th to 12th

Prince Loomba - 4 years, 11 months ago

Its answer is 8

Prince Loomba - 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

Prince Loomba - 4 years, 11 months ago

Probably 10

Hemanth K - 4 years, 11 months ago

Read my answer. Its 8

Prince Loomba - 4 years, 11 months ago

Math	Appears as
Remember to wrap math in `\(` ... `\)` or `\[` ... `\]` to ensure proper formatting.
`2 \times 3`	$2 \times 3$
`2^{34}`	$2^{34}$
`a_{i-1}`	$a_{i-1}$
`\frac{2}{3}`	$\frac{2}{3}$
`\sqrt{2}`	$\sqrt{2}$
`\sum_{i=1}^3`	$\sum_{i=1}^3$
`\sin \theta`	$\sin \theta$
`\boxed{123}`	$\boxed{123}$