Theory:

Between any two rational numbers, there are countless or infinite rational numbers.
 
Find the rational number between 210 and 810.
Example:
 
Now, 310, 410, 510, 610, 710 are rational numbers between 210 and 810.
 
The number of these rational number between 210 and 810 is \(5\).
 
We can also write 210 as 20100 and 810 as 80100
 
Now, 21100, 22100, 23100, 24100, ……78100, 79100 are rational number between 210 and 810.
 
The number of these rational number between 21100 and 80100 is \(59\).
  
And also can express 210 as 200010000 and 810 as 800010000
 
Now, 200110000, 200210000, 200310000200410000, . . . , 799810000, 799910000 are rational number between 210 and 80100.
 
Thus, we get \(5999\) rational numbers between 200010000 and 800010000.