Jane Street interview question

89 ^ 2?

Interview Answers

Anonymous

20 May 2012

8100-179=7921

Anonymous

5 Jun 2012

Alternatively: 90*88 + 1 = 7200 + 720 + 1 = 7921. Alternatively again: 200*39 + 121 = 7800 + 121 = 7921. See Ars Calcula for the mental math trick: http://arscalcula.com/