This document consists of two major sections. The first of these is actually three units that look at applications of arithmetic to business. Basic pre-algebra mathematics is an assumed prerequisite. These units are titled: 367-The Real Numbers; 368-Fractions and Their Uses: Ratio and Proportion; and 369-Exponents: Powers and Roots. Each module concludes with a test. This material is designed for individual study, and seeks to review arithmetic fundamentals and present topics in elementary algebra which have direct application to problems in business and to the use of the computer to solve such problems. The second section of this document is a unit that views applications of decimal arithmetic and area formulas to business. The material was written to give interior design students a trial run through computations which underlie nearly every project in residential design. It is one of a set of modules prepared for a course in business mathematics, but is viewed as also appropriate for inclusion in an interior design course. (MP)