Estimation (Intro) — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. For 312 + 254, the front-end estimate uses 300 + 200.
Front-end estimation keeps the leading hundreds, so 254 becomes 200 for a quick sum.
2. Front-end estimate of 312 + 254 is 500.
300 + 200 = 500 gives a fast estimate that is close to the real answer 566.
3. For 428 + 331, keep 400 and 300 as the front-end parts.
Front-end estimation uses just the hundreds digit place, so 331 becomes 300.
4. Front-end estimate of 428 + 331 equals 700.
400 + 300 = 700, a quick estimate close to the real sum 759.
5. For 615 + 172, front-end uses 600 plus 100.
172 has 1 in the hundreds place so the front-end piece is 100.
6. Front-end estimate of 615 + 172 is 700.
600 + 100 = 700 estimates the actual sum 787 quickly.
7. For 583 - 241, the front-end estimate is 500 - 200.
241 has 2 in the hundreds place, so the front-end value is 200.
8. Front-end estimate of 583 - 241 is 300.
500 - 200 = 300, a quick estimate near the real difference 342.
9. Front-end estimation is faster than adding the full numbers.
Front-end estimation skips the tens and ones so you can get a close answer faster in your head.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
312 + 254 front-end
→ 500
500
428 + 331 front-end
→ 700
700
615 + 172 front-end
→ 700 again
700 again
583 - 241 front-end
→ 300
300
Matching each problem to its front-end estimate shows how keeping only the hundreds gives a fast, close guess.