Number: Place Value, Operations, and Estimation
What you must understand
Grade 3 number work centres on place value to 1000, comparing and ordering numbers, adding and subtracting with and without regrouping, and beginning multiplication and division. You should be able to read and write numbers in standard, expanded, and word form, identify the value of a digit, round to the nearest ten or hundred, and connect multiplication to repeated addition and to arrays. Fractions appear as equal parts of a whole or a set, and you should compare simple fractions with the same numerator or denominator.
Traps to watch for
- Regrouping errors: when subtracting across a zero (e.g., 403 − 178), you must borrow twice; many answers are off by ten or one hundred.
- Place-value confusion: in 572, the 7 means 70, not 7.
- Operation mix-ups: "how many more" signals subtraction, while "how many in all" signals addition; word problems often hide the operation.
- Rounding direction: 450 rounds to 500 but 449 rounds to 400; look at the digit to the right of the target place.
- Fraction size: 1/8 is smaller than 1/4 even though 8 is bigger than 4.
Worked example
A class has 246 stickers and uses 129. How many remain? Line up place values: 6 − 9 needs regrouping, so borrow from the tens: 16 − 9 = 7. The tens column is now 3 − 2 = 1. The hundreds are 2 − 1 = 1. The answer is 117. Check by adding: 117 + 129 = 246, so the subtraction is correct.
Rule of thumb
Always estimate first (round to friendly numbers), compute exactly, then compare your answer to the estimate. A large gap signals a regrouping mistake.