Simple calculation is the focus of fourth grade mathematics and the question type that opens the gap in the exam. This 100-question exercise covers all the operation laws such as the law of multiplication distribution, the law of addition and the law of combination. After mastering, the calculation problem is fast and accurate.
Why is the same question, some children are fast and right, some are slow and wrong? The difference is whether or not to use the laws of computation. The fourth-grade “Law of Computation” unit is a watershed moment for elementary school computing skills.
Three Laws Mouth Art
- Additive commutative law: a + b = b + a; Additive conjugative law: (a + b) + c = a + (b + c);
- Multiplication commutation law: a × b = b × a; multiplication combination law: (a × b) × c = a × (b × c);
- Multiplication distribution law: a × (b + c) = a × b + a × c (the most common test).
Simple calculation in three steps
One look: observe the characteristics of the numbers (whether they can be rounded up, whether they have the same factors); two thoughts: think about which law to use; three calculations: deform the expression before calculating. For example, 25 × 4 × 8, 25 × 4 = 100, and then × 8 = 800, mental arithmetic can produce results.
Error-prone alerts
The multiplication distribution law is the most error-prone: a × (b + c) = a × b + a × c, every item in parentheses must be multiplied, and missing one is wrong. Tips for judging right and wrong: Check whether the results are reasonable after calculation. For example, 99 × 13 uses (100-1) × 13 = 1287. If you calculate 1300, it must be wrong.
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