This edition represents a significant revision of previous editions. A large number of new tasks were placed, and in order not to increase the excessive size of the Collection, a certain number of secondary tasks had to be removed. Thus, this edition of the Collection contains 1363 tasks, of which 364 are new, while in the previous edition there were only 1140 tasks. The numbering of tasks in connection with this has been changed, but in order to facilitate the use of old editions available in a large number in libraries of higher educational institutions, the number that the task had in the fourteenth and fifteenth editions is indicated in parentheses; naturally, the newly placed tasks are equipped with one number.