Quick counting: Thirty simple mental counting techniques

Currently, there are no manuals on the market containing instructions for quickly performing mental arithmetic operations. We therefore found it useful to collect in a short brochure the most simple and easily learned techniques for quick mental counting. They are... designed for average abilities and do not have in mind public performances on the stage, but the needs of everyday life. Those using the book should remember that successful mastery of its instructions presupposes not mechanical, but quite conscious use of techniques and, in addition, more or less lengthy training. But, having mastered the recommended techniques, you can perform quick calculations in your head with the accuracy of written calculations.