There are three envelopes and exactly two statements are written on each of the envelopes. The statements on one of the envelopes are BOTH TRUE, the statements on the other envelope are BOTH FALSE and the remaining envelope has ONE TRUE and ONE FALSE statement. Here is what is written on the three envelopes:

First Envelope:
(a)The formula is not in here.
(b)The formula is in Envelope 2.

Second Envelope:
(a)The formula is not in Envelope 1.
(b)The formula is in Envelope 3.

Third Envelope:
(a)The formula is not in here.
(b)The formula is in Envelope 1.

Which envelope contains the formula ?

We want the statements on the three envelopes to evaluate to TT, FF, and TF (or FT) for the correct location of the formula.

If the formula were in the first envelope, Then the statements on the three envelopes are:
1-FF, 2-FF, 3-TT. This cannot be the case.

If the formula is in evelope 2, the statements evaluate to:
1-TT, 2-TF, 3-TF. This is also not it.

With the formula in envelope 3, the statements are then:
1-TF, 2-TT, 3-FF; the formula must be in envelope three.

Posted by DJ on 2003-04-10 02:51:15