From 2n = 10× 0.008, n=25,

The stem leaf diagram shows that the median score of sampling test is 73.

The number of people with scores between [80,90] is 25-(2+7+ 10+2)=4.

The number of participants in the math contest is n=25, and the median is 73. The number of participants with scores within [80,90] and [90, 100] is 4 and 2 respectively.

(2) Let "two students within [80, 100] be selected, and just one of them has a score within [90, 100]" as the event m,

Number the four people in [80,90] as A, B, C and D; The two people in [90, 100] are numbered A and B.

The basic events in [80, 100] are: ab, ac, ad, aA, aB, bc, bd, bA, bB, cd, cA, cB, dA, dB, AB*** 15.

Among them, the scores of eight basic events are [90, 100], namely aA, aB, bA, bB, cA, cB, dA, dB and * * *.

So the probability is p (m) = 8 15.

A: The probability that a person's score is within [90, 100] is 8 15.