Question

estimate: 502 - 487 is about ______
calculate: 502 - 487 =
is your estimate reasonable? circle one. yes no

Explanation:

Estimate:

Step1: Round numbers

Round 502 to 500 and 487 to 490 (or 500 for simpler estimate). Let's use 500 - 490 or 500 - 500. Wait, better: 502 ≈ 500, 487 ≈ 490. So 500 - 490 = 10. Or 502 ≈ 500, 487 ≈ 490, so 500 - 490 = 10. Alternatively, 502 - 487: 502 is close to 500, 487 is close to 490, so 500 - 490 = 10. Or 502 - 487 ≈ 500 - 490 = 10 (or 502 - 487 ≈ 500 - 490 = 10, or even 500 - 487 ≈ 13, but let's do 502 ≈ 500, 487 ≈ 490: 500 - 490 = 10.

Step2: Calculate actual value

502 - 487: 502 - 487 = 15. Wait, wait, 502 - 487: 502 - 400 = 102, 102 - 87 = 15. So actual is 15. Wait, my estimate was 10, which is close to 15? Wait, maybe I rounded wrong. Let's re-estimate: 502 ≈ 500, 487 ≈ 490, 500 - 490 = 10. Or 502 ≈ 500, 487 ≈ 487, so 500 - 487 = 13. Then actual is 15, so 13 is closer. But the problem says "about". So estimate: 10 or 15? Wait, 502 - 487: 502 is 500 + 2, 487 is 500 - 13, so (500 + 2) - (500 - 13) = 2 + 13 = 15. Wait, no: 502 - 487 = (500 + 2) - (480 + 7) = 500 - 480 + 2 - 7 = 20 - 5 = 15. Oh! I made a mistake earlier. 502 - 487: 502 - 487 = 15. So let's re-estimate: 502 ≈ 500, 487 ≈ 490, 500 - 490 = 10. But actual is 15. Wait, maybe better to round 502 to 500 and 487 to 490: 500 - 490 = 10. But actual is 15. So the estimate of 10 is reasonable? Wait, 10 is close to 15? Maybe. Alternatively, 502 ≈ 500, 487 ≈ 487, so 500 - 487 = 13, which is closer to 15. But let's do the actual calculation first.

Calculate:

Step1: Subtract

502 - 487: 502 - 487. Let's do column subtraction:

502

• 487

------
15

Because: 2 - 7 can't do, borrow from 0, but 0 has to borrow from 5. So 5 becomes 4, 0 becomes 10, then borrow 1 from 10 to make 2 into 12. 12 - 7 = 5. Then the middle 0 (now 9) - 8 = 1. Then 4 - 4 = 0. So 0 1 5? Wait, no: 502 - 487:

5 0 2

• 4 8 7

--------
0 1 5? Wait, 5 - 4 = 1? No, wait, 502 is 5 hundreds, 0 tens, 2 ones. 487 is 4 hundreds, 8 tens, 7 ones.

Subtract ones: 2 - 7. Can't do, so borrow 1 ten from the tens place. But tens place is 0, so borrow 1 hundred from the hundreds place. So hundreds place: 5 becomes 4. Tens place: 0 becomes 10. Now borrow 1 ten from the tens place (10 becomes 9) to the ones place (2 becomes 12). Now ones: 12 - 7 = 5. Tens: 9 - 8 = 1. Hundreds: 4 - 4 = 0. So result is 15. So 502 - 487 = 15.

Estimate:

So estimate: 502 ≈ 500, 487 ≈ 490. 500 - 490 = 10. Or 502 ≈ 500, 487 ≈ 487, 500 - 487 = 13. Either way, 10 or 13 is close to 15? 10 is 5 less, 13 is 2 less. But the problem says "about". So estimate is about 10 (or 15? Wait, maybe I messed up. Wait, 502 - 487: 502 - 487 = 15. So estimate: 500 - 490 = 10, or 502 - 487 ≈ 15 (if we round 502 to 500 and 487 to 487, but that's not rounding). Wait, maybe the estimate is 10, and actual is 15, so the estimate is reasonable (since 10 is close to 15? Or maybe the estimate was 15? Wait, maybe I made a mistake in estimation. Let's try again: 502 is 500 + 2, 487 is 500 - 13. So (500 + 2) - (500 - 13) = 2 + 13 = 15. Oh! Wait, that's a better way. So 502 - 487 = (500 - 500) + (2 + 13) = 15. So actually, 502 - 487 = 15. So maybe the estimate is 15? Wait, but 502 is 500, 487 is 490, so 500 - 490 = 10. But actual is 15. So is 10 reasonable? 10 is close to 15, so yes.

Is your estimate reasonable?

Yes, because 10 is close to 15 (the actual value).

Answer:

s:
Estimate: 10 (or 15, but 10 is a common estimate)
Calculate: 15
Is your estimate reasonable? Yes (circle Yes)

Wait, let's confirm:

Estimate: 502 ≈ 500, 487 ≈ 490. 500 - 490 = 10. Actual: 15. 10 is close to 15, so the estimate is reasonable.

So:

Estimate: about 10 (or 15, but 10 is a typical estimate here)
Calculate: 15
Is your estimate reasonable? Yes.