Question: Product Codes

Comment on Product Codes

I understand that there are three different ways to arrange DDL. But I can't wrap my mind around the fact that since the digits are actually different, that when you arrange three different object there are actually 6 different ways.
So what is the logic behind the fact that there are 3 different ways with this question?
gmat-admin's picture

If you have 3 different objects to arrange, you can:
- Place the 1st object in one of 3 different locations (1st space, 2nd space and 3rd space)
- Place the 2nd object in one of the 2 remaining spaces
- Place the 3rd object in the 1 remaining space
So, the TOTAL # of arrangements = (3)(2)(1) = 6

Let's list them.
If there are three objects to arrange (A, B and C) we can create the following arrangements:

So why do we just count Digit1Digit2L, Digit1, L, Digit2 and L, Digit1, Digit2 as possibilities in this question, instead of the arrangements you just described?
gmat-admin's picture

I thought your question about arranging 3 objects was separate from the question on the video.
I don't quite understand your latest question. Can you please rephrase it?

Hi Brent,

In your second solution, we can solve using following way,

1. Select 2 Digit can also be solved as if order of two digit is important then it can be done = 5*4=20
2.Select One letter = 6
3. Arrange selected Letter in specific 2 digit by keeping order of digit important, this can be done in 3 ways, for ex if digit is 71 and letter is E then E can be placed as E71, 7E1, 71E. So a arrange letter in specific digit can be done =3

So answer is = 20*6*3=360.

What you think?

gmat-admin's picture

That's a perfectly valid approach - nice work!

That's what I love about GMAT math questions. They can often be solved in many different ways.
sir please explain
please explain
gmat-admin's picture

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