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.
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.
- Problems like this will appear on standardized tests like the SATs and ACTs.
|Number to divide by
||How to check
||Any number is divisible by 1
||2 = 1 + 1
||Any even number
||4 = 2 + 2
||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)
||The last two digits are divisible by 4.
||116: 16 is divisible by 4. (16/4)
||The last digit is a 5 or a 0.
||55: The last digit is a 5.
||The number is divisible by 2 and 3.
||36: Is divisible by 2. 3: 3 + 6 = 9 (9/3).
||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.
||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.
||The sum of all the digits is divisible by 9
||18: 1 + 8 = 9
||Use the way for finding threes
||The last digit is 0.
||150: The last digit is 0.