Explain how to estimate 458+322 two different ways

You could ignore the units which are the last digit of each number, so you add 45 and 32, then put a 0 on the end of your answer to give you 770. Or you could round off both numbers to the nearest 10, so 458 rounds up to 460 and 322 rounds down to 320, giving estimate of 780.

You can simply look at the number and guess. Rounded off it would then be about 800

You can also add the numbers first. You would get 780, you can then estimate from there. 800