Rules on Subject-Verb agreement are the most frequently asked questions about grammar and so let us start with the basics. Here are the rules.
Compound Subjects Rules:
Compound Subjects: All subjects joined by AND are plural.
Example: Rob and Lorie have decided to stay in school.
a. the compound subjects are synonyms or near synonyms or the second subject just restates, renames or duplicates the first subject.
Examples: wear and tear is, moaning and groaning is,
b. the two nouns joined by AND are generally considered as one.
Examples: Bread and butter, size and scope, extent and severity, pride and joy, sum and substance
c. the following compound subjects are generally regarded as singular: macaroni and cheese, fish and chips, pasta and sauce, oil and vinegar
d. compound subjects that are part of a single process are usually considered as singular
Examples: Buying and selling land is a lucrative business.
e. compound subjects preceded by the adjective every or each are considered singular.
Example: Every man and woman dreams of becoming successful.
NOTE: It is sometimes tricky to decide if the compound subjects can be taken as one or not. You can follow popular usage or just consider them plural when in doubt.