1ok .. prateek kam se kam answer toh aaya
abhi .. second one is wrong
The land of Hogwarts school of magic is different. The no. of girls and boys are equal . All the boys have two hands, while all the girls have only one {:)} . Dumbledore, the principal of the school arranged a party on new year's eve . According to the wishes of dumbledore all the boys and girls shook hands with everyone else in every possible way (i.e. left to left , right to right , left to right and right to left hand, all handshakes are permissible ) .
Q1. If the total number of handshakes that happened on new year's eve was 100, what is the population of the land ?
Q2. If there were 10 boys and 5 girls then what is the number of handshakes ?
Q3. Next day suddenly 5 death eaters with three hands arrived and again all wished each other including the people present earlier (actual population Q1. ) What is the total no. of handshakes ?
N.B. :
HIDE and post ur solution .. so that all of can try this question out .. i'll reply whether u r correct or not in ur chatbox ... :)
see post # 25
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34 Answers
1bas ulata sidha dimag lagaya...
main bhi correct method nahin de paoonga...
after 2 hrs of matha pachi ans aya hai...
1
13is the second one 290
edited
5 girls shake hand in 5C2 ways
10 boys shake hand in 4*10C2ways=180ways
each girl shakes 2 hands of a boy in 2ways 5*20=100ways
total 290 ways
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.
edited
131.
the equation if there are m boys and m girls
mC2+mC2*4+2m2
m=5
2m=10
1hey yaar why u hav taken 10C2 and 5C2 in solution of second part....
1abhi u r correct ... for details see my solution ...
let there be n boys and n girls
shakehands can be between boy and boy , boy and girl , girl and girl ...
two boys can shake hands in 4 ways .. both have 2 hands each
a boy and a girl can shake hands in 2 ways .. boy has 2 hands but girl only 1
two girls can shake hands in 1 way .. both have 1 hand each
so total no. of handshakes is ...
nC2 * 4 //2 boys selected
+ nC1 *nC1* 2 //1 boy 1 girl selected
+ nC2* 1 //2 girlss selected
=nC2 * 4 + nC1 *nC1* 2 + nC2* 1 = 100
.. now proceed answer is 5 boys n 5 girls .. total pop.. 10
13i have a better way to do the second one
total no. of hands 25
no. of ways of selecting two hands 25C2
10 ways in which we have considered shaking right hand with left
ans 300-10=290
13is the 3rd one 410
total hands 30
no. of choosing hands 30C2
in which 10 handshakes invalid for boys...... 5*3=15 invalid for death eaters
435-25=410
11type [50 ]
without the space and similar numbers upto 300 are new smileys
1http://targetiit.com/iit_jee_forum/posts/all_the_smileys_3653.html
visit this ..
1o .. no one is intrested .. ha .. [50]
yeh kya nautanki kar rahe ho .... smiley se important yeh question hai ...
1hello no one intrested .. yaar .. it is just simple P n C sum ....