Apply Number Sense to Problems

Number sense means understanding HOW numbers work — not just calculating answers. In this final Unit 1 lesson we pull all our skills together: place value, comparing, rounding, estimation, factors, multiples, and prime/composite numbers. Knowing which skill to use — and checking that the answer is reasonable — is what separates strong problem-solvers from calculators.

Strategy Selection

• Rounding → quick estimates when an exact answer is not needed.
• Mental math → speed; use number bonds, make-a-ten, or make-a-thousand.
• Place value → exact comparisons and column calculations.
• Factor / prime check → decide about divisibility or patterns.

Checking Reasonableness

• After solving, ask: "Is my answer in the right range?"
• Estimate first, then compare to your exact answer.
• If your estimate and exact answer are far apart, check your work.
• A reasonable answer does not have to be perfect — it must make sense.

Unit 1 Skills in One View

• Place Value: each digit has a value based on its position.
• Comparing: use place value to order large numbers.
• Rounding: find the nearest 10, 100, or 1,000.
• Estimation: round then calculate for a quick result.
• Factors & Multiples: lists of numbers that multiply to or from a given number.
• Prime & Composite: prime has exactly 2 factors; composite has more.