Using rounding or compatible numbers to estimate the sum 222 + 203 im a bit confuse of rounding to 5's

The easiest way I find of answering questions like these are to start with the numbers on the right and work left

So to answer 222+203 I would first do
2+3=5

Then
20+00=20

I would then add those two numbers up
20+5=25

I would then do 
200+200=400

And to finish off I would do
400+25=425

I find this method the easiest for working out a question like this.

I hope this has helped you.

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