Math Is Fun Forum

Pietwol

Member

Registered: 2012-03-08

Posts: 2

How many permutations?

I stumbled upon this wonderful site. I used to be able to do calcs about permutations, but not now. Too old. Help me with this one pleaaaase.

Our vehicle reg plates used to have a combination of three alpha and 3 numericals (excl. a,e,i,o and u)eg. BBB 123 (3x21 alpha and 3x10 nums) Now we have three sets of
2 alpa, 2 numbers and 2 alpha again (bb 11 bb) (2x21 alpha, 2x10 nums plus 2x21 alpha)

How the heck do I calculate the number of possible number plates???

Hope to hear from someone!!?

Piet

Bob

Administrator

Registered: 2010-06-20

Posts: 10,583

Re: How many permutations?

hi Pietwol

Welcome to the forum!   

2 alpa, 2 numbers and 2 alpha again (bb 11 bb) (2x21 alpha, 2x10 nums plus 2x21 alpha)

When you 'choose' the first alpha there are 21 possibilities.

When you choose the second, as a letter may be repeated, there are again 21 possibilities.

As every one of the first choice may be put with every one of the second that makes 21 x 21 possibilities.

Now do the same for the next numbers and letters and you get

21 x 21 x 10 x 10 x 21 x 21.

Hope that helps, 

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: How many permutations?

Hi Pietwol;

I am assuming you can use the same numbers and letters again after you have picked them.

Welcome to the forum.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Pietwol

Member

Registered: 2012-03-08

Posts: 2

Re: How many permutations?

Thanks guys. You make me feel rather stupid - it's so easy!!:|

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: How many permutations?

Hi Pietwol;

They are only easy when you get them right. They can be nightmares otherwise.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.