There are 31 days in January. January 21st 2015 was a Wednesday. What day of the week was February 8th 2015?

First we need to know how many days are still remaining before the end of January. In this case it would be 10 since 31-21=10. We know that 8th of February  is the 8th day of the month, so in total between January 21st and February 8th there are 18 (8+10) days. We know that every seventh day from January 21st would be Wednesday, so we divide 18 by 7 and we get 2 and 4 as a remainder. Thus February the 8th would be the fourth day after Wednesday, so it is Sunday.