Difference between revisions of "2014 UNCO Math Contest II Problems/Problem 2"

m (See also)
(Solution)
Line 12: Line 12:
  
 
== Solution ==
 
== Solution ==
 +
This is asking for the sum of 1-2+3-4...+289. We know that the sum of the first N even numbers is N^2+N. Because there are 144 even numbers less than 289, we take 144^2+144 and get 20880.
  
 
== See also ==
 
== See also ==

Revision as of 16:21, 23 December 2014

Problem

Define the Cheshire Cat function $\fbox{:)}$ by

\begin{align*}  \fbox{:)}(x) &= -x \quad \text {if } x \text{ is even and} \\ \fbox{:)}(x) &= x \quad \text{ if  }x \text{ is odd}  \end{align*}

Find the sum $\fbox{:)}(1) + \fbox{:)}(2) + \fbox{:)}(3) + \fbox{:)}(4) + . . .+ \fbox{:)}(289)$


Solution

This is asking for the sum of 1-2+3-4...+289. We know that the sum of the first N even numbers is N^2+N. Because there are 144 even numbers less than 289, we take 144^2+144 and get 20880.

See also

2014 UNCO Math Contest II (ProblemsAnswer KeyResources)
Preceded by
Problem 1
Followed by
Problem 3
1 2 3 4 5 6 7 8 9 10
All UNCO Math Contest Problems and Solutions