Tricks To Help Tell When Numbers Are Prime And Can`t Be Simplified

It is very important to be able to simplify fractions for full marks. As such, it is important to know how to tell if a number is prime or not. This is a list of tricks to use to tell what numbers can be divided by a single digit number:

2: The number is even

e.g: 6382

6382/2 = 3191

3: The digits in the number add up to a multiple of 3

e.g: 2793 ( 2 + 7 + 9 + 3 = 21)

2793/3 = 931

4: When halved, the new number is even

e.g: 6428 ( 6428/2 = 3214, which is even)

6428/4 = 1607

5: The number ends in 5 or 0

e.g: 1525

1525/5 = 305

6: The number is divisible by both 2 and 3. In other words, using our tricks, the number is even AND the digits of the number add up to a multiple of 3.

e.g: 3426 (divisible by 2, as it is even. Divisible by 3, as the digits add up to: 3+4+2+6 = 15)

3426/6 = 571

7: Unfortunately, there are no tricks to tell if a number is divisible by 7. Practice your 7 time`s tables until you get comfortable enough where you can spot these more easily

8: You halve the number twice, and the final number is even.

e.g: 6408 (6408 / 2 =3204, 3204 / 2= 1602. As the final number is even, 6408 is divisible by 8

6408/8 = 801

9: The digits in the number add up to 9. Additionally, any number divisible by 9 is divisible by 3.

e.g: 7299 (7+2+9+9 = 27)

7299/9 = 811

I hope you can understand these tricks. They`re very useful in non calc exams, and also calc exams where you`re running low on time and you need to ensure you`ve simplified your fractions as quickly as possible. Remember, every mark is so important!

Good luck with your studies and if you have any questions (about this article or any other questions) please don`t hesitate to get in touch!!