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Giuseppe adds all but one of the first 15 positive integers. His sum is a square of the excluded number. Which number did Giuseppe not include?

 Nov 29, 2021
 #1
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Let me correct the question first:

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Giuseppe adds all but one of the first 20 positive integers. His sum is a square of the excluded number. Which number did Giuseppe not include?

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The sum = 10.5 * 20 = 210

 

210 - 14 = 196

 

142 = 196

 Nov 30, 2021
 #2
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210 - x = x2

x2 + x - 210 = 0

x = 41,     x = - 15

Guest Nov 30, 2021
 #3
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Oops...cheeky

x = 14,   x = - 15   laugh

Guest Nov 30, 2021

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