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Sunday, May 17, 2015

Show with proof which of these two values is smaller: 7, or 2+5+11

Show with proof which of these two values is smaller:

7, or 2+5+11

I know this problem could be solved using numerous different methods but I am going to post my solution anyway, since I think and I believe I have done a great job in proving it using the most elementary method and the best of observation and thus it earned a place at this blog. :D

My solution:

Observe that

288<2892(122)<172 or (2<1712)(1)

80<815(42)<92 or (5<94)(2)

99<10011(32)<102 or (11<103)(3)

Adding the inequalities in (2), (2) and (3) up gives us the answer:

2+5+11<1712+94+103=7

Therefore, 2+5+11 is smaller than 7.

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