The manual provides material that will help develop mental counting skills on the basic topics of the second grade: "Addition and subtraction within 20", "Multiplication by 2, 3, 4", "Addition and subtraction of round numbers", "Addition and subtraction within 100”, “Multiply and divide by numbers from 1 to 5”, “Multiply and divide by numbers from 2 to 9”. Answering the teacher's questions for each of the above examples, students perform several mathematical tasks - more than 3,000 examples in total. Consistent completion of the tasks of the manual will help students master the skills of oral counting of all forms: fluent auditory counting (the teacher reads aloud a chain of examples , making small stops for counting, and the student answers after a few seconds), visual counting (chains of examples are written down, and the student either reports orally or writes down the answers), combined counting (the teacher dictates chains of examples, and the student writes down the answers).The systematic implementation of these tasks develops logical and mathematical thinking, ingenuity, strengthens memory and attention. At the discretion of the teacher, chains of examples can be used both for Olympiad works and tasks of increased complexity, and for repetition and consolidation of the studied topic. For better assimilation of the material, it is recommended to solve ten examples a day.The manual can be used in mathematics lessons and for independent work at home.