| Composite numbers | |
|---|---|
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| Description | |
| Exercise Name: | Composite numbers |
| Math Missions: | 4th grade (U.S.) Math Mission, Pre-algebra Math Mission |
| Types of Problems: | 1 |
The Composite numbers exercise appears under the 4th grade (U.S.) Math Mission and Pre-algebra Math Mission. This exercise practices recognition of composite numbers.
Types of Problems[]
There is one type of problem in this exercise:
- Find the composite number: This problem lists five numbers and asks the student to select the one that is a composite number.
Find the composite number
Strategies[]
This exercise is easy to get accuracy badges and speed badges because standard divisibility rules can be used to quickly discover which numbers are composite.
- The questions are multiple choice so there is only one correct answer. Once students find it, don't bother checking the other possibilities.
- Students can use this exercise to practice recognizing primes more easily, since each problem also lists four prime numbers.
Real-life Applications[]
- Problems like this will appear on standardized tests like the SATs and ACTs.
Divisibility Rules[]
| Number to divide by | How to check | Example | Note |
|---|---|---|---|
| 1 | Any number is divisible by 1 | 2 = 1 + 1 | |
| 2 | Any even number | 4 = 2 + 2 | |
| 3 | Add the digits together, if the number is divisible by 3, it is divisible by three. | 87: 8 + 7 = 15, 15 is divisible by three (15/3) | |
| 4 | The last two digits are divisible by 4. | 116: 16 is divisible by 4. (16/4) | |
| 5 | The last digit is a 5 or a 0. | 55: The last digit is a 5. | |
| 6 | The number is divisible by 2 and 3. | 36: Is divisible by 2. 3: 3 + 6 = 9 (9/3). | |
| 7 | Double the last digit and subtract the number from the rest of the number and get an answer that is divisible by 7. (including 0) | 7: 14, 14 - 7 = 7 | This strategy is one of the hardest. It would maybe be easier to try to divide. |
| 8 | The last three digits form a number divisible by 8. | 960: Is divisible by 8. | Another way: 96: divisible by 8 (8*12), annex the 0. |
| 9 | The sum of all the digits is divisible by 9 | 18: 1 + 8 = 9 | Use the way for finding threes |
| 10 | The last digit is 0. | 150: The last digit is 0. |