How could you missed those numbers?

Algebra Level 3

1 , 2 , 3 , … , 9 1,\ 2,\ 3,\ \ldots,\ 9

I added up the nine numbers above and got 23. I then realized that my calculation was wrong because I missed 3 of the 9 numbers.

Which of the following must be one of the 3 numbers I forgot to add?

6 7 8 9

Pi Han Goh by Pi Han Goh , 30, Malaysia

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2 solutions

Hana Wehbi
Aug 16, 2017

NIce problem. I actually like most of the problems you post.

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Joseph Wilson
Aug 14, 2017

Isn't the ordered triple of forgotten numbers [ 1 , 10 , 11 ] [1,10,11] a counter example to always having forgotten one of 6 , 7 , 8 , 9 6,7,8,9 ?

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Sorry. Fixed.

Pi Han Goh - 3 years, 10 months ago

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Thanks. Looks good now.

@Joseph Wilson In future, if you spot an issue with a problem, you can report it directly by selecting "Report problem" from the menu. This notifies the problem creator that something could be amiss.

Calvin Lin Staff - 3 years, 10 months ago

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Excellent, I'll make sure to do that next time.

Joseph Wilson - 3 years, 10 months ago

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