A Short Lesson on Tens-complements

    Here is a brief lesson on tens-complements. Eventually there will be an entire lesson on them, because they are so important.
   Until then, look at it this way - the tens-complement of any digit is the number you would need to make the number a ten. For instance, if you had the number 7, you would need 3 more to make it a 10. So three is the tens-complement of 7, and 7 is the tens-complement of 3.

• The tens complement of 1 is 9, and vice-versa,
• The tens complement of 2 is 8, and vice-versa,
• The tens complement of 3 is 7, and vice-versa,
• The tens complement of 4 is 6, and vice-versa,
• The tens complement of 5 is 5.

  Those are all the tens-complements. It is worth it to learn them, because there are hundreds of shortcuts in math which use them. I hope to cover most of them in this site, eventually.