Seems like it's saying the numbers were changed by the sum of the three 100s,

which means changed by 300 since
3 x 100 = 300.

Now changed by 300 can mean :

①Increased by 300

Or

② Decreased by 300

So think of three different 3 digit numbers first.


There are actually 6 possible permutations:

456
465
546
564
645
654

You can pick three and then do the following to each number :

① add 100
② subtract 100


So for example, the three I pick are
456,546,654.


Calculation ① : 456 + 100 = 556
Calculation ② : 456 - 100 = 356

Calculation ③ : 546 + 100 = 646
Calculation ④ : 546 - 100 = 446

Calculation ⑤ : 654 + 100 = 754
Calculation ⑥ : 654 - 100 = 554