I believe that is a very large number
250 + 100 = 350
It is: 100+250 = 350
250 as a percentage of 350 is 100*250/350 = 71.43% approx. It makes no difference whether that takes 5 months, 5 seconds or 5 millennia: the percentage is the same.
50, 100, 150, 200, 250, 300, 350, 400, 450, 500
350
50, 100, 150, 200, 250, 300, 350, . . .
250
50, 100, 150, 200, 250, 300, 350, . . .
50, 100, 150, 200, 250, 300, 350 . . .
100, 150, 200, 250, 300, 350, 400, 450 . . .
250 of 350 is 71.43%
50, 100, 150, 200, 250, 300, 350, 400 . . .