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Math Challenge II-B combinatorics 3.22

 
 
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Math Challenge II-B combinatorics 3.22
by Jialin Wang - Saturday, December 18, 2021, 2:56 PM
 

I'm not sure about what the "numbers" in the problem refers to. Does it refer to the digit or the number as a whole? e.g. If i want to erase 27, can I only erase the 2 or the 7? or am i required to erase both digits at once?

 
Picture of John Lensmire
Re: Math Challenge II-B combinatorics 3.22
by John Lensmire - Tuesday, December 21, 2021, 12:03 PM
 

You are erasing the entire numbers, not digits. A few examples looking at the sum $1+2+3$:

  • We could erase nothing to get $1+2+3 = 6$
  • We could erase everything to get $0$
  • We could erase the $2$ to get $1+3 = 4$,
  • We could erase $2$ and $3$ to get $1$
  • etc.

Basically you're adding up some/none/all of the numbers from the original sum and trying to figure out how many different sums are possible. Hope this helps!

 
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