If on 1 January 2020 was Wednesday, then what will be the day on 28 February 2021 ?

Sunday

\(\frac{Date + Month\;code + Century\;code + Century\;upper\;year + Quotient\;of\;\frac{upper\;year}{4}}{7}\) 

\(\frac{1 + 0 + 6 + 20 + 5}{7}\) = \(\frac{32}{7}\) = Remainder 4

In case of Leap Year the code for January and February is reduced by 1

so, remainder is 3

The day for Code 3 is Wednesday. So, it is the same day which is given

therefore,

The day for 28th february 2021 was :

\(\frac{Date + Month\;code + Century\;code + Century\;upper\;year + Quotient\;of\;\frac{upper\;year}{4}}{7}\) 

\(\frac{28 + 3 + 6 + 21 + 5}{7}\) = \(\frac{63}{7}\) = Remainder 0

The day for Code 0 is Sunday. 

Note:     

Code for      Mon – 1      Tues – 2      Wed – 3      Thurs – 4

                   Fri – 5         Sat ­­– 6        Sun – 0

Code for      Jan – 0        Apr – 6       July – 6       Oct – 0

                   Feb – 3       May – 1      Aug – 2       Nov – 3

                   Mar – 3       June – 4      Sep – 5       Dec – 5

Code for     

1900 is 0

2000 is 6

2100 is 4

2200 is 2

2300 is 0

2400 is 6

2500 is 4   and  Likewise