John beat his previous high score in the favorite game by 28%. If his new high score is 288 points, what was his previous high score?

Let x be the previous high score, that is initially 100%. John beat his previous high score in the favorite game by 28% and the new high score 288 points is 128%. Then you can write it as proportion:
[tex] \dfrac{x}{288} =\dfrac{100}{128} [/tex].
Solve it by cross multiplication:
[tex] 128x=288\cdot 100,\\ 128x=28800,\\ \ \\ x=\dfrac{28800}{128} ,\\ \ \\
x=225 [/tex].
Answer: the previous high score was 225 points.