Re: ISI 2014 PEA Answer Key

Posted by Amit Goyal on Apr 29, 2014; 4:07am
URL: http://discussion-forum.276.s1.nabble.com/ISI-2014-PEA-Answer-Key-tp7587867p7588020.html

For Q 7, we have to count the number of ways in which we can fill these seven spots using letters from {A, B, C} so that A cannot be followed by B, B cannot be followed by C, and C cannot be followed by A
_ _ _ _ _ _ _
First spot can be filled by any of the three letters, i.e. in three ways. Once the first spot is filled, we have only two ways to fill the second spot. For example, if the first spot is filled by A, then second spot will be taken by either A or C. Similarly for the third spot and so on. So there are 3(2^6) = 192 ways.