## A.10 Summation Basics

$$123 = 3 \times 1 + 2 \times 10 + 1 \times 100$$

• Value of a number depends on digits it consists of

Arrangements of 1, 2, 3

123

132

231

213

312

321

In all places, each digit is repeated twice (2!)

Sum = 2!(1+2+3)1+2!(1+2+3)10+2!(1+2+3)100 = 2!(1+2+3)(1+10+100)