Initial number that is given in the question = 280
Final number that is given in the question = 289
Total amount of increase in the number = 289 - 280
= 9
Then
Percentage of increase in the given number = (9/280) * 100
= 90/28
= 45/14
= 3.21 percent
So the percentage increase in the number is 3.21%. I hope the procedure is clear enough for you to understand. This will help you to solve similar problems with ease in future.