Estimation: Your Math Superpower

Rounding Estimation

Question 1

Score: 0

Estimation: Your Math Superpower

What Is Estimation?

Estimation is finding a value close enough to the exact answer—essentially a smart guess.

Key Methods Covered

• Rounding Numbers
• Front-End Estimation
• Real-life applications

Rounding Rules

Nearest Ten

Look at the ones digit:

• 0-4 → Round DOWN
• 5-9 → Round UP

Replace the ones digit with 0. Example: 42 → 40.

Nearest Hundred

Look at the tens digit:

• 0-4 → Round DOWN
• 5-9 → Round UP

Change tens and ones to 0. Example: 2596 → 2600.

Nearest Thousand

Look at the hundreds digit:

• 0-4 → Round DOWN
• 5-9 → Round UP

Change hundreds, tens, and ones to 0. Example: 7503 → 8000.

Quick Reference Chart

Number	Nearest Ten	Nearest Hundred	Nearest Thousand
68	70	100	0
482	480	500	0
869	870	900	1,000
3,259	3,260	3,300	3,000
9,745	9,750	9,700	10,000

Estimation with Rounding — 3 Steps

1. Round each number.
2. Compute using the rounded values.
3. Sense-check against the exact answer.

Worked Examples

Addition: 763 + 136

Round → 800 + 100 = 900  
Exact  → 899 ✔ close!

Subtraction: 846 – 694

Round → 800 – 700 = 100  
Exact  → 152 ✔ reasonable

Front-End Estimation

Use only the leading digit for a lightning-fast estimate.

1. Keep the first digit; change others to 0.
2. Add or subtract these new numbers.

Example: 324 + 219 → 300 + 200 = 500 (exact = 543).

Front-End vs Rounding

2,468 + 3,579:

• Rounding: 2,500 + 3,600 = 6,100
• Front-End: 2,000 + 3,000 = 5,000
• Exact: 6,047

Rounding is closer here (only 53 away).

Range of Possible Values

“About 400 students” covers 350-449 when rounding to the nearest hundred.

Mini Formula Cheat-Sheet

• RoundDown(place) = (digit_at_place) × place
• RoundUp(place) = (digit_at_place + 1) × place
• FrontEnd(n) = leading_digit × 10^(digits-1)
• Estimate(sum) = Σ rounded_or_frontEnd(numbers)

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