Divisibility rules for 7,13,17,19 (prime numbers) || mathssupport

#mathssupport #divisibility

[Meghism]

Why is the last number multiplied with 2 everytime ?

[suyajnamech]

Thank you so much ... Tomorrow is my maths exam

Can you prove the divisibility rule with 17?

[wrc]

For whatever it's worth there is another rule that works for 7, 11 and 13. It is to arrange the digits in groups of 3 then do an alternating sum.

E.g if the number is 341709123 you do the following:

123 - 709 + 341 = -245

Now you can do the 24 - 2x5 to get 14 and show it is a multiple of 7.

Not all that practical, I know because would involve a lot of 3 digit addition and subtraction in your head (though there are some tricks to make it easier with some practice), but it can still come in handy.

For example suppose you have the number 16989. Rather than doing the method shown in this video 3 times you could instead start out with

989 - 16 = 973

Now you can do 97 - 2x3 = 91, etc.

[MohitRajput-pjmu]

You are best teacher fore deciding rue

[jaimelerpido]

Where did you get the numbers -2, +4, -5, +2, and +7 for the corresponding numbers 7, 13, 17, 19 and 23?

[govindsinghyadav]

Sir, why this rule doesn't apply for all prime number.

[skp]

Check your 13 divisibilty rule for following the +4 rule for 2002

[wairimugrace]

You said the code is -2. Why aren't you multiplying the last digit by -2?

[anirbanbhattacharyya]

In each case how we can find the remainder if it's not divisible?

[sivakumarbilla]

Divisibility rule of 23 is not work out