What is the sum of all digits of $\color{#D61F06}{10}^{\color{#3D99F6}{20}}-\color{#624F41}2$ ?

The answer is 179.

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10^20-2 this means

10000...(20 times 0)

subtract 1 means 20 times 9

subtract 2 means 19 times 9 and then 8

i.e, 19X9+8

171+8

179