SOLUTION: HOW TO SOLVE MENTALY THIS IN 5 SECONDS 68*69

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Question 422309: HOW TO SOLVE MENTALY THIS IN 5 SECONDS 68*69
Answer by ewatrrr(24785) About Me  (Show Source):
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Hi

HOW TO SOLVE MENTALY THIS IN 5 SECONDS 68*69

the 'Quick' Idea is based on 68*69 = (70-2)(70-1) = 4900-3*70 +2 ..4690 + 2

     4692