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kapsycumm
n is a positive integer, and k is the product of all integers from 1 to n inclusive.
If k is a multiple of 1440, then the smallest possible value of n is

A. 8
B. 12
C. 16
D. 18
E. 24

Factorizing 1440, we get \(2^5 * 3^2 * 5^1\)

So, k should have at least five 2s, two 3s and one 5.

a) 8! = 2*3*4*5*6*7*8. Above condition is satisfied. Hence answer is A
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Took me 0:37 to do 1440x2 and divide that by the smallest choice to see if it fit. 2880/8=360, so A.

(I know my methods are unorthodox, but what can you do.)
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rockzom
Took me 0:37 to do 1440x2 and divide that by the smallest choice to see if it fit. 2880/8=360, so A.

(I know my methods are unorthodox, but what can you do.)

'Unorthodox' is one way of putting it. :)

I'm not sure I understand why you've done what you did, but we're not looking here for the smallest answer choice which divides some multiple of 1440; it's coincidence that you get the right answer if you try that. If '4' or '5' had instead been the first answer choice, you'd find that 2880/4 or 2880/5 is an integer, but those aren't correct answers to the question. There's a reason Bunuel and Karishma carried out the steps they did.
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kapsycumm
n is a positive integer, and k is the product of all integers from 1 to n inclusive.
If k is a multiple of 1440, then the smallest possible value of n is

A. 8
B. 12
C. 16
D. 18
E. 24

K= multiple of 1440 ie product of some integer P X 1440. &
K= n! = 1.2.3.4......n

Now lets factorize 1440 = 12 * 12 * 10
Now my objective is to find this multiple 12*12*10 with min possible numbers in n!. Lets go on now......
n= 1*2*(3*4)*5*6*7*8(4 X 2)
Hence 8! is sufficient to get a multiple of 12*12*10

Hence Answer A.
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n is a positive integer, and k is the product of all integers from 1 to n inclusive. If k is a multiple of 1440, then the smallest possible value of n is

A. 8
B. 12
C. 16
D. 18
E. 24

Let’s break 1440 into prime factors:

1440 = 144 x 10 = 12 x 12 x 10 = 2^5 x 3^2 x 5^1

Thus, k/(2^5 x 3^2 x 5^1) = integer.

We also know that k is the product of all integers from 1 to n inclusive, or in other words, k = n!.

Let’s check our answer choices:

A. If n = 8, then k = 8! and 8! = 8 x 7 x 6 x 5 x 4 x 3 x 2 = 2^3 x 7 x 3 x 2 x 5 x 2^2 x 3 x 2 = 7 x 5 x 3^2 x 2^7 does contain five 2s, two 3s and one 5.

Answer: A
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Hope, this illustration will work.

Posted from my mobile device
Attachments

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Factorise 1440 : = 10 X 144
2x5 x 12 x 12
2X5x 3 x 4 x 6 x 2
1 x 2x3x 5 x 6 x 8 ( to get consequtive number 1 to n = you need 4 and 7
Now K is the Multiple of 1440 : There fore K can be = 1440 x 28
and also 1 x 2 x 3x4x5x6x7x8 = 1440 X 28
So n should be latest : 8
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n is a positive integer, and k is the product of all integers from 1 to n inclusive which means k = n!

K is a multiple of 1440 => k = 1440 * p

1440 = 2*2*2*2*2*3*3*5

=> 1440 = \(2^5\) * \(3^2\) * 5

n! = \(2^5\) * \(3^2\) * 5 * p

We need at least five (2's), two(3's) and one(5)

=> 8! = 8 * 7 * 6 * 5 * 4 * 3 * 2 = 2 * 2 * 2 * 7 * 2 * 3 * 5 * 2 * 2 * 3 * 2 = \(2^5\) * \(3^2\) * 5 * \(2^2\) * 7 = 1440 * \(2^2\) * 7

Answer A
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shrive555
n is a positive integer, and k is the product of all integers from 1 to n inclusive. If k is a multiple of 1440, then the smallest possible value of n is

A. 8
B. 12
C. 16
D. 18
E. 24

The question tells k! is divided by \(1440\)

So k have to have all the factors that \(1440\) will have.

\(The \ factors \ of \ 1440=2^5, 3^2\ & \ 5\)

From the answer choices \(8!\) contains \(= 8 * 7 * 6 * 5 * 4 * 3 * 2 = 2 * 2 * 2 * 7 * 2 * 3 * 5 * 2 * 2 * 3 * 2=2^7, 3^2, 5, \ & \ 7\)

The answer is \(A.\)
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Hey are these type of questions still relevant in 2024?
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Rangerwarrior
Hey are these type of questions still relevant in 2024?
This particular question is very much in the syllabus of GMAT Focus.
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­Take the time to get it right. Have to see the factors of 1440 and then walk up the factorials until you get the lowest factorial that covers all the factors of 1440:

­
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I have a question here that i'm wondering if someone can help me answer.
In my head i knew that 6! = 720 which 720 * 2 = 1440 hence the smallest value of would be n! = (4 * 6!)
Keeping this in mind, is there a way to get from (4 * 6!) to 8! without going through prime factorization?
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georgia123
I have a question here that i'm wondering if someone can help me answer.
In my head i knew that 6! = 720 which 720 * 2 = 1440 hence the smallest value of would be n! = (4 * 6!)
Keeping this in mind, is there a way to get from (4 * 6!) to 8! without going through prime factorization?

6! = 720, so we need one more 2.

The next number, 7!, will add 7, which does not have a factor of 2. However, 8!, will have a factor of 2. That's how we get 8!.
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Prime Factorizing of 1440, we get
2^5*3^2*5
There must have 5 2s. That is only possible in 8!
Answer:A

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First factor out the 1440 = 2^5 * 3^2 * 5

Now of the answer choices, which factorial not only shares the same primes but is the lowest option?

8! = 8*7*6*5*4*3*2*1 = 2^7 * 3^2 * 5 * 7
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