Sunday, May 11, 2014

Problem

There are 4 cards on a table. Each has a number on one side and a letter on the other. The cards show A,B,1 and 2. Which 2 cards would you turn over to test the rule that "All cards with a vowel on one side have an even number on the other".

Solution

A and 1, since by elimination...

1.we have to take A as if there is a odd no.. back of A then our rule get's violated so without picking A we can't be sure that our rule holds good.

2. B we can leave since it doesn't satisfy the rule at all, doesn't have a vowel so it really doesn't matter whether it has a even number on the other side; eliminate it.

3. 2, also we can eliminate since if it has a consonant on the other side..then also...our rule doesn't violate..since converse of our rule is not true..(if it a even no. on one side then it has to have a vowel on the other). However if 2 has a vowel on the other side..then our rule holds good..so without picking 2 we can be sure that our rule would hold good in case of 2; hence eliminate that.

4. 1, however we can't go away with 1; since if it has a VOWEL on the back side..then our rule would violates..so we can be sure by picking 1 along with A to make sure..that

hence Ans = A,1

References