Here’s the answer to yesterday’s practice question, thanks for sending in all of your answers!

offers hundreds of practice questions and video explanations. Go there now.

Magoosh GRE Blog Everything you need to know about the GRE

By Margarette Jung on February 8, 2012 in Combinations and Permutations, Math Concepts, Math Multiple Choice, Math Question Types, Practice Question of the Week, Video Tips and Explanations

Here’s the answer to yesterday’s practice question, thanks for sending in all of your answers!

**Magoosh blog comment policy**: To create the best experience for our readers, we will only approve comments that are relevant to the article, general enough to be helpful to other students, concise, and well-written! 😄 Due to the high volume of comments across all of our blogs, we cannot promise that all comments will receive responses from our instructors.

We highly encourage students to help each other out and respond to other students' comments if you can!

If you are a Premium Magoosh student and would like more personalized service from our instructors, you can use the Help tab on the Magoosh dashboard. Thanks!

Hi Chris,

If the question ask that password will be at least 9 digits number then what will be the answer? 18*9!

Hi Spondon,

Do you mean minus the repeating constraint, i.e., a number can repeat? If so, then the answer would actually be 9^9 x 10^9. Again, I’m not quite sure what you are asking, but I hope that helps :).

no repeating constraint. just for the significant 9 or 10 digits “number” password. because in some arrangement the starting number will be “0”. I am asking for this case.

Thanks

Spondon

Hi Spondon,

Hmmm…I’m still not quite sure what you are asking. Could you take another stab at rephrasing your question :).

Hi, I have a question regarding why it is 2 x 10! Since the question ask for permutation of at least 9 digits, which is 9x8x… and so on. Why is it necessary to do this twice? If it’s also 10X9x and so, then it could also be 11x10x9, and so on. In theory, it could also be 3x 10! or 4x 10! So where I fail to understand is how do we know from the question that it should be 2 x 10! and not 3 x 10! etc ? Thanks.

Hi Jim,

The twist to this problem is the number zero. The password requires a digit and there are 10 digits, including zero: 0, 1, 2, 3…9.

The question also states that the password has to be at least 9-digits long. So we have two possible passwords: a 9-digit password and a 10-digit password. Each has 10! different passwords so we get 2 x 10!.

Hope that helps 🙂

Thanks Chris! I just signed up for the Magoosh premium service. Will be taking my GRE for the first time hopefully in the upcoming first weeks of April. To say I have an anxiety for taking the GRE would be an understatement. I’ve been putting it off for over 2 years now, I would’ve had my masters by now, lol. I’ve taken College GRE prep course when the old GRE was was in circulation. I have to say that, that prep course wouldn’t have helped me much particularly in the Quant section, it was 6 weeks long and barely scratching the surface! It didn’t help with most of the complex problems.

So having signed up for Magoosh, hopefully it will prepare me in 30-35 days. I would like to devote 15 hours a week for 4 to 5 weeks and take my first attempt. Hope to at least get in the above 150 range on each section, that’s my target, not too unrealistic, but not too pessimistic either. Because I know that if I plan it out for 2 to 3 months, I would never be focused for the long haul and miss the deadline for fall admission, once again!

Hi Jim,

Sounds like a good plan! I agree – it’s a lot easier to stick to an agressive 30-day plan than it is a 2-3 month plan.

I think you will be happy with Magoosh’s quant – we help you become confident in all the fundamentals in the lesson videos. Then you apply that knowledge to question that go from the easy to the mind-blowing-ly complex.

I think your 15 hr. plan should def. get you to 150+ in each section. You may want to take the PowerPrep II test in the next couple of weeks to see where you are scoring.

Let me know if I can answer any other questions :).

Hi,

As I understand the password here is supposed to be atleast 9 digit long.

So isn’t 012345678 considered as an 8 digit number? If yes, then I think the possible 9 digit passwords would be 9 x 9! and possible 10 digit ones would be 9 x 9!. Do correct me if I am wrong. Thanks!

Hi Kalyani,

012345678 has nine digits including the zero. Of course in number land that would not be a valid number (no integer, besides ‘0’, starts with a zero). In password land you can start with a zero.

Hope that helps!

Yes, Order matters in this case.

Because 123456789 and 987654321 are two different passwords.