Answer: There is a 75% increase from 400 to 700.
Step-by-step explanation: If 400 is considered 100%, then 800 would be considered 200%. Using this information, we can infer that 400 to 800 is a 100% increase. Now, using this information, 700 is a jump by 300 from 400, versus 800 (a jump by 400 from 400). We now know that 300 out of 400 is 75%, meaning that the increase from 400 to 700 is 75%.