Mother\textquotesingle s Day in $$2020$$ was May $$10^{\rm th}$$, which was a Sunday. Father\textquotesingle s Day in $$2020$$ was June $$21^{\rm st}$$. On what day of the week did Father\textquotesingle s Day fall? 
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There are in total $$21 + 21 = 42$$ days from May $$11$$ to June $$21$$. Since $$42 \div 7 = 6$$, with no remainder, the Father\textquotesingle s Day falls on Sunday as well. 