Two possible answers are:
Rounding to the nearest ten, we have 590-320 = 270; rounding to the nearest hundred, we have 600-300 = 300.
Explanation:
When estimating, we can round the number to different places. Both numbers are in the hundreds place. This means we can round to either the hundreds or the tens place.
Rounding 586 to the tens place, 8 is in the tens place. Looking behind it, we have a 6; this means we round the 8 up to 9, and have 590.
Rounding 321 to the tens place, 2 is in the tens place. Looking behind it, we have a 1; this means we keep the 2 and have 320.
590 - 320 = 270.
Rounding 586 to the hundreds place, 5 is in the hundreds place. Looking behind it, we have an 8; this means we round the 5 up to 6 and have 600.
Rounding 321 to the hundreds place, 3 is in the hundreds place. Looking behind it, we have a 2; this means we keep the 3 and have 300.
600-300 = 300.
