Logic Puzzles

4. Two Condoms, Three Partners

You are about to have intercourse with three consenting adult partners, one after another. Exactly two of them are HIV-positive and one is HIV-negative, but you do not know which is which until the moment you are with that partner.

You have exactly two condoms. A condom may be reused, but any surface that has touched an HIV-positive partner (or another surface that has) will certainly transmit the virus to the next HIV-negative person it contacts. You must plan the order of use, putting on, removing, turning inside-out, etc., so that when all three acts are finished no HIV-negative person (including yourself) has been exposed to the virus.

Is it possible, and if so, how?

Added 4 August 2008

Hint:

Think of the two condoms as two layers you can rearrange. Try to keep one surface that never touches an infected partner until the very last moment.

Solution:

Yes, it is possible. Number the condoms C₁ (inner) and C₂ (outer):

  1. Put on C₁, then pull C₂ over it (double-layer).
  2. Have intercourse with the first partner. If this partner is HIV-positive, only the outside of C₂ is contaminated.
  3. Remove C₂ and set it aside (its outer surface may be contaminated).
  4. Keeping C₁ on, have intercourse with the second partner. If this partner is HIV-positive, only the outside of C₁ is now contaminated; its inner surface (still against your skin) is clean.
  5. Turn C₂ inside-out so that its previously clean inner surface is now on the outside, and pull it back over C₁.
  6. Have intercourse with the third partner.

Throughout the process exactly one condom surface that has never touched an HIV-positive partner (the former inside of C₂) is the only surface that contacts the HIV-negative partner. Therefore no uninfected person is exposed.


Comments (4)

sperman 23 January 2013

Is there a real answer dude? Wont u tell it :/

tartle 24 January 2013

There is a real answer.

thejoanzone 2 August 2013

Use one condom on two of the prostitutes, faking an orgasm with the first. If the second one protests, she's AIDS free.

sai teja 2 October 2013

make sex with the 3rd person.who had no AIDS

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