Answer: She wrote [tex]3\dfrac{1}{20}[/tex] documents on Friday.
Step-by-step explanation:
GIven: Total documents needed to be done = 12
If she finished writing all documents by Friday, then the number of documents written on Friday = 12-(work done by Wednesday) - (work done on Thursday)
[tex]= 12 -(3\dfrac15)-(5\dfrac34)\\\\=12-\dfrac{16}{5}-\dfrac{23}{4}\\\\=\dfrac{12\times20-16\times4-23\times5}{20}\\\\=\dfrac{240-64-115}{20}\\\\=\dfrac{61}{20}\\\\=3\dfrac{1}{20}[/tex]
Hence, She wrote [tex]3\dfrac{1}{20}[/tex] documents on Friday.