Calendar – Railway Reasoning

tuesday
Formula for calculating day of any date
0 = sunday, 1 = monday.... 6 = saturday
A = century code (4, 2, 0, 6 for remainder
1, 2, 3, 0)dividing the first two digit of the year by 4
B = last two digits of year
C = number of leap years fallen in that century before that date.
D = month code (respective code of the months are 0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5)
E = date
Day = remainder of (A + B + C + D + E) when divided by 7.
For 1 september 2020,
A = 6 B = 20 C = 5 D = 5 E = 1
According to formula,
Remainder of( 𝐴 + 𝐵 + 𝐶 + 𝐷 + 𝐸 )/7 = 37/7  is 2
2 stands for tuesday.

sunday
Formula for calculating day of any date
0 = sunday, 1 = monday.... 6 = saturday
A = century code (4, 2, 0, 6 for remainder 1, 2, 3, 0) dividing the first two digit of the
year by 4
B = last two digits of year
C = number of leap years fallen in that century before that date.
D = month code (respective code of the months are 0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5)
E = date
Day = remainder of (A + B + C + D + E) when divided by 7.
For 1 march 2020,
A = 6 B = 20 C = 5 D = 3 E = 1
According to formula,
Remainder of ( 𝐴 + 𝐵 + 𝐶 + 𝐷 + 𝐸 )/7 = 35/7 is 0
0 stands for Sunday. 

monday
5 feb 2018 → Monday
So , on
5 feb 2019 → Monday +1 = tuesday
Number of odd days from 5 feb 2019 to 8
april 2019 → 23 + 31 + 8 = 6 odd days.
8 april 2019 →
tuesday + 6 days = Monday