Hi there!
[tex]81*20=4\frac{1}{20}[/tex]
Let see how much 20 goes into 80:
[tex]20,40,60,80[/tex]
That would be 4 time...
Subtract terms with terms:
[tex]81-80=1[/tex]
Remainder would be 1.
Convert term into fraction:
[tex]\frac{1}{20}[/tex]
Final Result:
[tex]4\frac{1}{20}[/tex]