Was or Were
Twelve dollars in single bills (was/were) all she had in her wallet.
Were
The correct form is "were."
"Twelve dollars in single bills were all she had in her wallet."
The correct form to use in this sentence is "was." Here's how you can determine this:
In this case, the subject is "Twelve dollars," which is a plural noun because it refers to more than one dollar bill. Typically, when the subject is plural, we use the verb form "were." However, in this specific sentence, we are referring to the amount of money as a singular amount, rather than the individual bills. So, even though "dollars" is plural, we treat it as a singular noun in this context.
To confirm, you can try replacing "twelve dollars" with a singular noun phrase like "an amount." The sentence would then read: "An amount in single bills was all she had in her wallet." Now it becomes apparent that "was" is the correct form to use because we are talking about a singular amount.
Therefore, the sentence should be written as: "Twelve dollars in single bills was all she had in her wallet."