Question

estimate: 918 - 829 is about
calculate: 918 - 829 =
is your estimate reasonable?

Explanation:

Estimate:

Step1: Round the numbers

Round 918 to 920 and 829 to 830.

Step2: Subtract the rounded numbers

$920 - 830 = 90$
So, 918 - 829 is about 90.

Calculate:

Step1: Subtract the units digits

8 - 9, we can't do that, so we borrow 1 from the tens place. The 1 in the tens place becomes 0, and the 8 in the units place becomes 18. Then $18 - 9 = 9$.

Step2: Subtract the tens digits

Now the tens place has 0 (after borrowing), so we borrow 1 from the hundreds place. The 9 in the hundreds place becomes 8, and the 0 in the tens place becomes 10. Then $10 - 2 = 8$.

Step3: Subtract the hundreds digits

$8 - 8 = 0$.
Putting it all together, $918 - 829 = 89$.

Is your estimate reasonable?

The estimate was 90 and the actual result is 89. The difference between the estimate and the actual result is 1, which is very small. So the estimate is reasonable.

Answer:

s:

• Estimate: 90
• Calculate: 89
• Is the estimate reasonable: Yes