1993 UNCO Math Contest II Problems/Problem 1

Problem

How many times must one shoot at this target, and which rings must one hit in order to score exactly $100$ points?

$[asy] draw(circle((0,0),1),black); draw(circle((0,0),2),black); draw(circle((0,0),3),black); draw(circle((0,0),4),black); draw(circle((0,0),5),black); draw(circle((0,0),6),black); MP("40",(0,0-.3),N); MP("39",(0,1-.1),N); MP("24",(0,2-.1),N); MP("23",(0,3-.1),N); MP("17",(0,4-.1),N); MP("16",(0,5-.1),N); [/asy]$

Solutions

Solution 1

We can try combinations of numbers that add to $100$ . We soon find that one must shoot at the target $6$ times and hit the $16$ ring $2$ times and hit the $17$ ring $4$ times.

Solution 2

Since $100=2^2\cdot5^2$ , we can take $\pmod25$ and $\pmod4$ of the $6$ numbers. From $\pmod25$ we have the set (in order) ${15,14,-1,-2,-8,16}$ , and from $\pmod4$ we have the set ${0,-1,0,-1,1,0}$ . We notice that as $8$ is $1/2$ times $16$ , we probably have two times more $17$ s than $16$ s, and it works perfectly, so one has to shoot the $16$ ring $2$ times and the $17$ ring $2$ times.

1993 UNCO Math Contest II (Problems • Answer Key • Resources)
Preceded by First Question	Followed by Problem 2
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10
All UNCO Math Contest Problems and Solutions

Page

Toolbox

Search

1993 UNCO Math Contest II Problems/Problem 1

Contents

Problem

Solutions

Solution 1

Solution 2

See also