How do you estimate the sum by rounding?

Answer 1

for example, 555+325. let's say we want to round this to the nearest hundred. first you find the digit in the hundreds place, i would like to mark it. then you look to the right, you would probably want to draw an arrow. then if the digit is five or more round up, if it's less than five round down. ok, 555, you look to the right since the digit to the right is five or more round up. so you round up to 600. for 325, the digit to the right is 2, so you round down. round down to 300. ok, that was the rounding part. now you have to estimate the answer. 600+300=900. that's the answer.