Add sequences of numbers in the 10's

1. Choose a 2-digit number in the 10's. To add all the 10's from 10 up through this number and down from it:
2. Square the 2nd digit of the number
   (keep the carry)   _ _ X
3. The number of terms is 2 x the 2nd digit + 1.
4. The first digits = the number of terms
   (+ carry). nbsp; X X _

   Example:

1. If the 2-digit number in the 10's selected is 16:
   (10 + 11 + 12 ... 16 + 15 + 14 ... 10)
2. Square the 2nd digit of the number:
   6 x 6 = 36 (keep carry 3)   _ _ 6
3. No. of terms = 2 x 2nd digit + 1:
   2 x 6 + 1 = 13
4. No. of terms (+ carry): 13 + 3 = 16   1 6 _
5. So the sum of the sequence is 166.

   See the pattern?

1. If the 2-digit number in the 10's selected is 18:
   (10 + 11 + 12 + ... 18 + 17 + 16 + 15 ... 10)
2. Square the 2nd digit of the number:
   8 x 8 = 64 (keep carry 6)   _ _ 4
3. No. of terms = 2 x 2nd digit + 1:
   2 x 8 + 1 = 17
4. No. of terms (+ carry): 17 + 6 = 23   2 3 _
5. So the sum of the sequence is 234.