Re: ISI 2014 PEA Answer Key

Posted by Varun on May 06, 2014; 10:18am
URL: http://discussion-forum.276.s1.nabble.com/ISI-2014-PEA-Answer-Key-tp7587867p7588741.html

For q 25..it is one of d standard prob based on "'Pigeon hole principal' ."
soluiton in detail :max n min no of handshakes(HSs) a person can do = 19 & 1 respectively (u can't handshake urself.)

Assume for a moment, a random person ,say , A shook hand wid B n leaves d party implying A being one of d person to have shaken hand in odd number i e 1 in dis case.

now, max HS B can do  is 19(18 +1) while for odrs would be 18 (since A is gone home,nly 19 members r left)

For d sake of argument,to make all HS even,  lets say dat B does HS wid wid 17 ppl in party leaving C, dat way his total handshakes are 17 + 1 = 18 now. Now out of18 ppl( excluding A B ) , odr than C, everyone HS wid 17 making der total HS to 18 .(still even). but for B, d max HS can only b 17 ( A is gone n B refused) making his HS always odd.in total A n C have shaken hand wid odd ppl.

Dis way,  der cant be '1' person to have shaken hand wid odd no off ppl,wtever way u try. Since 1 cant b answer, option D is not d answer implyiing option C as answer.( u dun need to check for 19, sicne der is only 1 correct ans)...

For more details, u can refer to 'Pigeon hole principal' .