Q: Given a text, write a compressed version of it in a single sentence.
As mail volume increases in postal systems, variable costs (processing and transportation) increase and fixed costs decrease as a percentage of total costs. Therefore, street delivery costs, which are largely fixed, decrease as a percentage of total costs as volume increases.
A:
As mail volume increases in postal systems, variable costs increase and fixed costs decrease as part of total costs. Thus, street delivery costs decrease as percentage of total costs as volume increases.