Daily Aptitude Questions and Logical Puzzles

[ssh]

i know that we have to use permutation and combination, but i have forgot them.. (last learnt on my 12th).. need answer with some explanation..

[tush_8600]

Even I have forgotten.. I had solved this by trial and error method.
For simplicity, assume only 4 people, A, B, C,D, have done handshakes. so total no. of handshakes=AB+AC+AD+BC+BD+CD
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Similarly if 5 people, total no. of handshakes=AB+AC+AD+AE+BC+BD+BE+CD+CE+DE
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From above two, total no. of handshakes of 'n' people= addition of first (n-1) numbers.
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So answer is 12

[tush_8600]

Today's Question:
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Answer will be posted tomorrow.