3000 * 2/ 10 = 600- number of elderly people

3000 * 3/10 = 900-the number of middle-aged people.

3000 * 5/ 10 = 1500- number of young people

Then use the old number *K to get the old number that should be drawn out.

Youth middle age ditto

Then the calculated numbers are randomly selected from the elderly, middle-aged and young people.