. x=45×0.05+55×0. 15+65×0.2+75×0.3+85×0.25+95×0.05═72
So it is estimated that the average score of this exam is 72.
(2) The number of all possible basic results of the numbers 95, 96, 97, 98, 99 and 100 is C62= 15, and there are 15 results.
The number of students with [90, 100] is 0.005× 10×80=4.
These two figures are just the basic results of two students' math scores, C42=6.
The probability that two numbers are exactly the math scores of two students is p = 6 15 = 25.