Question

Math brain teaser!

Answer 1

At a party, everyone shook hands with everybody else. There were 66 handshakes. How many people were at the party?

Answer 2

lets say there are only 3 people
A,B,C

then how many handshakes ?

Answer 3

I know the answer and how to solve it, its just a fun brain teaser :3

Answer 4

A with, B and C , thats 2
and B with C, thats 1

so total = 2+1
for 3 people
====

similarly for 'n' people, you get
1+ 2+3+ ... (n-1)

Answer 5

which is
n(n-1)/2

Answer 6

66 = n(n-1)/2

find n
i am too lazy to calculate it :P

Answer 7

Ummm, something like\[
{n\choose 2} = 66
\]

Answer 8

http://www.wolframalpha.com/input/?i=%28n+choose+2%29+%3D+66

Answer 9

n(n-1) = 132 = 11 *12
which obviously gives you
n =12

Answer 10

There were negative 11 people.

Answer 11

lol

Answer 12

hhh

Answer 13

12

In general, with n+1 people, the number of handshakes is the sum of the first n consecutive numbers: 1+2+3+ ... + n.
Since this sum is n(n+1)/2, we need to solve the equation n(n+1)/2 = 66.
This is the quadratic equation n2+ n -132 = 0. Solving for n, we obtain 11 as the answer and deduce that there were 12 people at the party.

Since 66 is a relatively small number, you can also solve this problem with a hand calculator. Add 1 + 2 = + 3 = +... etc. until the total is 66. The last number that you entered (11) is n.

Answer 14

@drumminboy918 If I come up one with one, can you solve it?

Answer 15

Probably not, I am terrible at math. But I will try.

Answer 16

I have a few more that are really fun!

Answer 17

@wio lets be in separate Qn

Answer 18

What?! @ikram002p ?!

Answer 19

i thought ur gonna type a Qn -_- nvm