Khan/khan-exercises — Issue #12044: Counting 2 - counting2
Author: KhanBugz
Created: 2012-01-25 01:32:35+00:00
State: open
Labels: safari, snowleo, wrong-or-unclear

if there are ten people in a room only 50 hand shakes occur because, 1 shakes the hands of peoples 2.3.4.5.6.7.8.9.10 and 2 only shakes the hands of peoples 3.4.5.6.7.8.9.10 and 3 only 4.5.6.7.8.9.10, and so on so its like adding numbers 9+8+7+6+5+4+3+2+1

[counting_2.html?seed=66&problem=handshakes](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/counting_2.html?seed=66&problem=handshakes&debug)

[Answer timeline](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/counting_2.html?seed=66&problem=handshakes&debug&activity=%5B%5B%22incorrect-activity%22%2C%22%5C%2250%5C%22%22%2C13%5D%2C%5B%22incorrect-activity%22%2C%22%5C%2250%5C%22%22%2C3%5D%2C%5B%22hint-activity%22%2C%220%22%2C9%5D%2C%5B%22hint-activity%22%2C%220%22%2C13%5D%2C%5B%22hint-activity%22%2C%220%22%2C15%5D%2C%5B%22hint-activity%22%2C%220%22%2C29%5D%2C%5B%22incorrect-activity%22%2C%22%5C%2290%5C%22%22%2C49%5D%2C%5B%22incorrect-activity%22%2C%22%5C%2290%5C%22%22%2C2%5D%2C%5B%22incorrect-activity%22%2C%22%5C%2290%5C%22%22%2C3%5D%2C%5B%22incorrect-activity%22%2C%22%5C%2290%5C%22%22%2C4%5D%5D)

["50","50","90","90","90","90"]

Mozilla/5.0 (Macintosh; Intel Mac OS X 10_6_8) AppleWebKit/534.51.22 (KHTML, like Gecko) Version/5.1.1 Safari/534.51.22

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