Math New Drill (Level 3) : Round off the 3rd digit number from the top of the 123rd power of 2

I round off the 3rd digit number from the top of the number of 123rd power of 2. 

Find two digits number from the top of this number.

Answer 

11

Noted

Solution

2^10 = 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 × 2 = 1024

2^20 = (2^10)×(2^10)
           = 1024 × 1024 
           = 1048576

2^40 = (2^20) ×(2^20)
           = 1048576 × 1048576
2^40 ~~ 1048000 × 1048000 = 1098304000000

2^123 = (2^41) × (2^41) × (2^41) 

　　　　 = (2^40 × 2) × (2^40 × 2) × (2^40 x 2)
2^40 × 2 ~~ 1098304000000 × 2 = 219600-------.

219600----- ~~ 220000---.

2^123 ~~ (220000---) × (220000---) × (220000---) 

            ~~ 1064800------.
Round off the 3rd digit number of 1064800-------, then it is 1100000------.