What will be the day of the week on 15 August 2021 ?

15th August, 2021 = (2020 years + Period 1.1.2021 to 15.8.2021)

Odd days in 1600 years = 0

Odd days in 400 years = 0

20 years = (5 leap years + 15 ordinary years) = (5 x 2 + 15 x 1) = 25 = 4 odd days 

Jan. Feb. March April May June July Aug. (31 + 28 + 31 + 30 + 31 + 30 + 31 + 15) = 227 days

227 days = (32 weeks + 3 days) = 3 odd days

Total number of odd days = (0 + 0 + 7 + 3) = 7 = 0 odd days

Given day is Sunday.