How to Find Prime Numbers In A Chart of 1 to 100?

Elementary Math (K-6th) Tutorial

How to Find Prime Numbers In A Chart of 1 to 100?


Finding prime numbers in a chart of 1 to 100 can be helpful to memorize and to understand with dealing with small numbers. However, a chart would not be practical for doing homework, a quiz, or a test. Nevertheless, the steps that I have provided in dealing with numbers from 1 to 100 is a basic way to find the prime numbers and the composite numbers, with the exception of 1.

Sample Problem

Suppose I have a chart from 1 to 100. Which numbers should I circle that are prime numbers? Which numbers should I cross out that are composite numbers?


1. Cross off 1.
2. Circle 2 and cross off every multiple of 2 like 4,6,8,10,12,…
3. Circle 3 and cross off every multiple of 3 like 6,9,12,15,18,…
4. Circle 5 and cross off every multiple of 5 like 10,15,20,25,30,…
5, Circle 7 and cross off every multiple of 7 like 14,21,28,35,42,…
6. Circle every number that is not crossed out.
-Make sure to cross out the 1 and the multiples of 2,3,5, and 7 before circling everything that is not crossed out.

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