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Difference between revisions of "2009 UNCO Math Contest II Problems"

(Created page with "University of Northern Colorado MATHEMATICS CONTEST FINAL ROUND January 31,2009. For Colorado Students Grades 7-12. ==Problem 1== How many positive <math>3</math>-digit number...")
 
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have this property but <math>245</math> and <math>317</math> do not.
 
have this property but <math>245</math> and <math>317</math> do not.
  
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[[2009 UNC Math Contest II Problems/Problem 1|Solution]]
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[[2009 UNCO Math Contest II Problems/Problem 1|Solution]]
  
 
==Problem 2==
 
==Problem 2==
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(b) For how many <math>n</math> between <math>1</math> and <math>100</math> inclusive is <math>R_n=1^n+2^n+3^n+4^n</math> a multiple of 5?
 
(b) For how many <math>n</math> between <math>1</math> and <math>100</math> inclusive is <math>R_n=1^n+2^n+3^n+4^n</math> a multiple of 5?
  
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[[2009 UNCO Math Contest II Problems/Problem 2|Solution]]
  
 
==Problem 3==
 
==Problem 3==
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smallest number of ants that could be in the army?
 
smallest number of ants that could be in the army?
  
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[[2009 UNCO Math Contest II Problems/Problem 3|Solution]]
  
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==Problem 4==
 
  
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How many perfect squares are divisors of the product <math>1!\cdot 2!\cdot 3!\cdot 4!\cdot 5!\cdot 6!\cdot 7!\cdot 8!</math> ? (Here, for
 
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example, <math>4!</math> means <math>4\cdot 3\cdot 2\cdot 1</math>)
 
  
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[[2009 UNC Math Contest II Problems/Problem 4|Solution]]
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[[2009 UNCO Math Contest II Problems/Problem 4|Solution]]
  
 
==Problem 5==
 
==Problem 5==
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</asy>
 
</asy>
  
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[[2009 UNCO Math Contest II Problems/Problem 5|Solution]]
  
 
==Problem 6==
 
==Problem 6==
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<asy>
 
<asy>
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draw((0,0)--(0,4),arrow=Arrow());
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draw((0,0)--(0,3),arrow=Arrow());
 
draw((0,0)--(4,0),arrow=Arrow());
 
draw((0,0)--(4,0),arrow=Arrow());
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for(int x=0;x<;,++x){
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for(int x=0;x<4;++x){
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for(int y=0;y<2;++y){
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for(int y=0;y<3;++y){
 
D((x,0)--(0,y),black);
 
D((x,0)--(0,y),black);
 
}}
 
}}
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</asy>
 
</asy>
  
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[[2009 UNC Math Contest II Problems/Problem 6|Solution]]
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[[2009 UNCO Math Contest II Problems/Problem 6|Solution]]
  
 
==Problem 7==
 
==Problem 7==
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by <math>x-3.</math> What is the remainder when <math>P(x)</math> is divided by <math>(x+2)(x-3)</math>?
 
by <math>x-3.</math> What is the remainder when <math>P(x)</math> is divided by <math>(x+2)(x-3)</math>?
  
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[[2009 UNC Math Contest II Problems/Problem 7|Solution]]
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[[2009 UNCO Math Contest II Problems/Problem 7|Solution]]
  
 
==Problem 8==
 
==Problem 8==
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</asy>
 
</asy>
  
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[[2009 UNC Math Contest II Problems/Problem 8|Solution]]
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[[2009 UNCO Math Contest II Problems/Problem 8|Solution]]
  
 
==Problem 9==
 
==Problem 9==
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</asy>
 
</asy>
  
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[[2009 UNCO Math Contest II Problems/Problem 9|Solution]]
  
 
==Problem 10==
 
==Problem 10==
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(c) generalize for any <math>n</math>.
 
(c) generalize for any <math>n</math>.
  
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[[2009 UNCO Math Contest II Problems/Problem 10|Solution]]
  
 
==Problem 11==
 
==Problem 11==
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\end{align*}</cmath>
 
\end{align*}</cmath>
  
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[[2009 UNC Math Contest II Problems/Problem 11|Solution]]
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[[2009 UNCO Math Contest II Problems/Problem 11|Solution]]
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== See Also ==
 +
{{UNCO Math Contest box|year=2009|n=II|before=[[2008 UNCO Math Contest II]]|after=[[2010 UNCO Math Contest II]]}}

Revision as of 18:40, 20 May 2021

University of Northern Colorado MATHEMATICS CONTEST FINAL ROUND January 31,2009.

For Colorado Students Grades 7-12.

Problem 1

How many positive $3$-digit numbers $abc$ are there such that $a+b=c$ For example, $202$ and $178$ have this property but $245$ and $317$ do not.

Solution

Problem 2

(a) Let $Q_n=1^n+2^n$. For how many $n$ between $1$ and $100$ inclusive is $Q_n$ a multiple of $5$?

(b) For how many $n$ between $1$ and $100$ inclusive is $R_n=1^n+2^n+3^n+4^n$ a multiple of 5?

Solution

Problem 3

An army of ants is organizing a march to the Obama inauguration. If they form columns of $10$ ants there are $8$ left over. If they form columns of $7, 11$ or $13$ ants there are $2$ left over. What is the smallest number of ants that could be in the army?

Solution



Solution

Problem 5

The two large isosceles right triangles are congruent. If the area of the inscribed square $A$ is $225$ square units, what is the area of the inscribed square $B$?

[asy] draw((0,0)--(1,0)--(0,1)--cycle,black); draw((0,0)--(1/2,0)--(1/2,1/2)--(0,1/2)--cycle,black); MP("A",(1/4,1/8),N); draw((2,0)--(3,0)--(2,1)--cycle,black); draw((2+1/3,0)--(2+2/3,1/3)--(2+1/3,2/3)--(2,1/3)--cycle,black); MP("B",(2+1/3,1/8),N); [/asy]

Solution

Problem 6

Let each of $m$ distinct points on the positive $x$-axis be joined to each of $n$ distinct points on the positive $y$-axis. Assume no three segments are concurrent (except at the axes). Obtain with proof a formula for the number of interior intersection points. The diagram shows that the answer is $3$ when $m=3$ and $n=2.$

[asy] draw((0,0)--(0,3),arrow=Arrow()); draw((0,0)--(4,0),arrow=Arrow()); for(int x=0;x<4;++x){ for(int y=0;y<3;++y){ D((x,0)--(0,y),black); }} dot(IP((2,0)--(0,1),(1,0)--(0,2))); dot(IP((3,0)--(0,1),(1,0)--(0,2))); dot(IP((3,0)--(0,1),(2,0)--(0,2))); [/asy]

Solution

Problem 7

A polynomial $P(x)$ has a remainder of $4$ when divided by $x+2$ and a remainder of $14$ when divided by $x-3.$ What is the remainder when $P(x)$ is divided by $(x+2)(x-3)$?

Solution

Problem 8

Two diagonals are drawn in the trapezoid forming four triangles. The areas of two of the triangles are $9$ and $25$ as shown. What is the total area of the trapezoid?

[asy] draw((0,0)--(20,0)--(2,4)--(14,4)--(0,0),black); draw((0,0)--(2,4)--(14,4)--(20,0),black); MP("25",(9,.25),N);MP("9",(9,2.25),N); [/asy]

Solution

Problem 9

A square is divided into three pieces of equal area by two parallel lines as shown. If the distance between the two parallel lines is $8$ what is the area of the square?

[asy] draw((0,0)--(1,0)--(1,1)--(0,1)--cycle,black); draw((1,0)--(0,2/3),black); draw((1,1/3)--(0,1),black); [/asy]

Solution

Problem 10

Let $S=\left \{1,2,3,\ldots ,n\right \}$. Determine the number of subsets $A$ of $S$ such that $A$ contains at least two elements and such that no two elements of $A$ differ by $1$ when

(a) $n=10$

(b) $n=20$

(c) generalize for any $n$.

Solution

Problem 11

If the following triangular array of numbers is continued using the pattern established, how many numbers (not how many digits) would there be in the $100^{th}$ row? As an example, the $5^{th}$ row has $11$ numbers. Use exponent notation to express your answer.

\begin{align*} &1 \\ &2 \\ 3\quad &4\quad 5\quad \\ 6\quad 7\quad &8\quad 9\quad 10\quad \\ 11\quad 12\quad 13\quad 14\quad 15\quad &16\quad 17\quad 18\quad 19\quad 20\quad 21\quad \\ 22\quad 23\quad 24\quad 25\quad 26\quad 27\quad 28\quad 29\quad 30\quad 31\quad &32\quad 33\quad 34 \quad 35\quad 36\quad 37\quad 38\quad 39\quad 40\quad 41\quad 42\quad \\ \cdot \quad &\cdot\quad \cdot\quad \\ \end{align*}

Solution

See Also

2009 UNCO Math Contest II (Problems • Answer Key • Resources)
Preceded by
2008 UNCO Math Contest II 		Followed by
2010 UNCO Math Contest II
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10
All UNCO Math Contest Problems and Solutions
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