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Composite numbers

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Composite numbers
Composite numbers 256
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:

  1. Find the composite number: This problem lists five numbers and asks the student to select the one that is a composite number.
    Compnum

    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.

  1. The questions are multiple choice so there is only one correct answer. Once students find it, don't bother checking the other possibilities.
  2. Students can use this exercise to practice recognizing primes more easily, since each problem also lists four prime numbers.

Real-life Applications

  1. 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.

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