Hello there.
Question: Write an equation that models the sequence: 200, 500, 1250
Answer: I got 2x + x/2.
200 x 2 = 400.
200 /2 = 100
400 + 100 = 500.
It does fit the pattern.
In short, your answer is 2x + x/2.
Hope This Helps You!
Good Luck Studying ^-^