To start to figure this problem out, we can first figure out how many more pages you read in an hour compared to your sister.
50 - 40 = 10, so you read 10 more pages in 1 hour. 
Now we have to figure out how much more you would read in 1/2 an hour. Since 1/2 an hour is 1/2 of an hour, we can divide 10 by 2 to figure out how many more pages you read in an hour compared to your sister. 10 divided by 2 is 5, so you read 5 more pages every half hour.
 
        
             
        
        
        
Answer:
0^6= 1000000. The final answer is 25000000.
 
        
             
        
        
        
Arctan (√3 /3) = 30°. = π/6 rad
That is the value searched, in degrees and radians.
You can verifiy that tan(30°) = sin(30°) / cos(30°) = [1/2] / [√3/2] = 1/√3 = √3 / 3