MathDB
all p + 1 numbers are equal

Source: 6th QEDMO problem 5 (22. - 29. 8. 2009) https://artofproblemsolving.com/community/c1512515_qedmo_200507

May 8, 2021
algebra

Problem Statement

Let pp be a prime number and let further p+1p + 1 rational numbers a0,...,apa_0,...,a_p with the following property given: If one removes any of the p+1p + 1 numbers, then the remaining may be split in at least two groups , which all have the same mean value (for different distant numbers, however, these mean values ​​may be different). Prove that all p+1p + 1 numbers are equal.