# Thread: contradiction problem

1. ## contradiction problem

Very tricky contradiction problem:-

Basketball player Michael keal's team statistician keeps track of the number, S(N), of the successful free throws he has made in the first N attempt of the season. Early in the season, S(N) was less than 80% of the N, but by the end of the season S(N) was more than 80% of the N. Was there necessarily a moment in between when S(N) was exactly 80% of N?
Use proof by contradiction and assume there was no such moments. Then S(N) much jump over 80% at one time....

2. Originally Posted by Vedicmaths
Very tricky contradiction problem:-

Basketball player Michael keal's team statistician keeps track of the number, S(N), of the successful free throws he has made in the first N attempt of the season. Early in the season, S(N) was less than 80% of the N, but by the end of the season S(N) was more than 80% of the N. Was there necessarily a moment in between when S(N) was exactly 80% of N?
Use proof by contradiction and assume there was no such moments. Then S(N) much jump over 80% at one time....
If there is no such moment then some time in the season there exists a number of free throws $\displaystyle N$ where the number of successes was $\displaystyle M$ and

$\displaystyle \frac{M}{N}<0.8$

but the next free throw was a success and:

$\displaystyle \frac{M+1}{N+1}>0.8$

The first of these inequalities may be rearranges to:

$\displaystyle M-0.8N<0$

and thesecond to:

$\displaystyle M-0.8N>0.8$,

but $\displaystyle M-0.8N$ canot be both less than $\displaystyle 0$ and greater than $\displaystyle 0.8$, a contradiction, hence the assumption is false and there must be a point in the season where $\displaystyle S(N)=80\%$

RonL