This is very simple. The main thing is that you need to understand how to change non-standard normal distribution into standard normal distribution.

(90-70)/ root number 100 obeys the standard normal distribution, and it is found that 0.977 people are less than 2 in the standard normal distribution, that is, 1000*0.977=977 people are below 90 points, and 23 people are above 90 points.

You can look at the bottom. Normal distribution is very important, but the college entrance examination will not be too difficult. Basic standardization must be mastered! !