Radhika is 83 weeks and 6 days older than me, whereas John is 72 weeks and 7 days older than Radhika. If John was born on a Sunday, on which day of the week was I born?
John is 83 + 72 = 155 weeks and 6 + 7 = 13 days older than me. Weeks are in multiples of 7 days. So we can ignore them. We can deal with the 13 days alone. Since 13 = 1 X 7 + 6, the excess days are 6. So we can count the day to Sunday + 6 = Saturday..