(1) Based on the properties of the rectangular table of frequency distribution, the sum of all frequencies should be 1, which can be obtained as follows: a =1-(0.015+0.125+0.5+0.3/kloc-0.

(2) There are graphs and several definitions, which can be obtained by means of frequency formula: through probability P ≈ 162200 = 0.8 1.

(3) From the definition of average in statistics, we can get the average score of this math exam. x = 10×3+30× 10+50×25+70× 100+90×62200 = 70.7。