Can someone please explain this to me ?
Eg 1986 is four different numbers
5 Answers

We all agree 1987 consists of 4 different numbers. 1,9,8, and 7. 1988 and 1989 won’t work because the eight and nine are repeated, meaning the year couldn’t have 4 different numbers. (1,9,8,8 and 1,9,8,9). None of the 90’s will work because you would automatically have two repeating numbers (19901999). The same for the 00’s. (20002009). 2010 doesn’t work because of the two repeating 0’s, 2011 doesn’t work because of the two repeating 1’s, and 2012 doesn’t work because of the two repeating 2’s. Making 2013 the first year since 1987 to have 4 different numbers.

1986 was before 1987… 2013 is the first one since 1987. Meaning after 1987.

1986 does have four different numbers. However, your question states SINCE 1987, not prior to 1987.

Every year after 1987, the year had repeated numbers. Like, 1988 has two eights. That kind of thing continued to happen until 2013.

1987: Four different numbers (1,9,8 and 7)
1988: Double 8’s
19891990: Double 9’s
1991: Double 1’s and 9’s
19921998: Double 9’s
1999: Triple 9’s
2000: Triple 0’s
2001: Double 0’s
2002: Double 2’s and 0’s
20032010: Double 0’s
2011: Double 1’s
2012: Double 2’s
2013: Four different numbers (2, 0,1 and 3)
See what I mean? The next time well have two same digits is in the 2020’s decade and the next time to have four different digits again is in 2031.