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How many hand shakes if 12 people shake hands with every other person in room?
72
Seven people shake hands once how many times do they shake hands?
For everyone to shake hands with everyone else, there are 21 handshakes. (below copied from my answer of a similar question) This is an arithmetic progression and can be solved with the equation Sn=(1+(n-1))(n-1)/2 where Sn is the total sum of handshakes for n people. NB: I have used n-1 instead of n in the equation for the sum of an arithmetic progression, because you're not really going to shake hands with yourself, so you don't include the nth term, in this case 7. Alternatively, you can solve this geometrically by drawing a heptagon, drawing lines between all the vertices, and then adding all the lines up.
If There are 5 people at a party Each person must shake hands once with every other person at the party How many handshakes does it take to do this?
10 times
How many cedar shakes are in a square?
A "square" of shakes covers 100 SF of wall or roof area. Beyond that - everything depends on the installation. The number of actual pieces of wood in a square varies greatly based on the exposure the installer wants to leave, and the width of the shakes, which are normally bundled random in width. A single handsplit shake is going to be 18" in length and be installed with an exposure anywhere from 4"-7" . It could be anywhere from 3-12" in width. It typically takes 4-6 bundles of shakes to get 100SF of exposure, but again that varies wildly based on the product and how it is installed. Note that cedar "Shakes" are typically hand-split and will vary greatly- whereas cedar "shingles" are machine cut and can be ordered in uniform width if desired.
Seven people meet and shake hands with one anotherHow many handshakes occur?
The first person can be selected in one of seven ways. Having selected him, the second can be selected from the remaining six in six ways. So there would appear to be 7*6 ways of selecting the couples shaking hands. But, x shaking y's hand is the same handshake as y shaking x's hand. Thus each handshake is conted twice, So the total number of handshakes is 7*6/2 = 21
