Answers

2014-11-10T21:20:38+08:00
101 can be expressed as 100 + 1
99 can be expressed as 100-1

(a+b)(a-b) = a^2 - b^2

(100 + 1)(100 - 1) = 100^2 - 1^2 = 10000 - 1 = 9999
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