Estimating and Adding

We round the summands to the nearest tenth. Remember:

▶If the number ends in 0, 1, 2, 3 or 4, we round of down.

▶If the number ends in 5, 6, 7, 8 or 9, we round of up 

We add the rounded numbers

We look at the total amount of rounding. three things can happen:

▶If we’ve rounded one amount up and one down, the sum we have obtained is a correct estimation.

▶If both summands have been rounded up and the amount of rounding is greater than 5, we subtract 10 from the estimate.

▶If both summands have been rounded down and the amount of rounding is greater than 5, we add 10 to the estimate.