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Math Expert V
Joined: 02 Sep 2009
Posts: 58434
If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Question Stats: 51% (01:38) correct 49% (01:36) wrong based on 632 sessions

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Tough and Tricky questions: Factors.

If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

(A) 2
(B) 3
(C) 6
(D) 8
(E) 10

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Re: If p ^3 is divisible by 80, then the positive integer p must  [#permalink]

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ggarr wrote:
If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

2
3
6
8
10

Prime factorize $$80 = 2^4 * 5$$
If $$p^3$$ has at least four 2s and a 5, it must have at least six 2s and three 5s (Every prime factor of $$p^3$$ must have a power which is a multiple of 3).
So p must have at least two 2s and a 5 as factors.

Minimum value of $$p = 2^2 * 5$$
This gives us $$(2+1)*(1+1) = 6$$ distinct factors (at least)
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Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Bunuel wrote:

Tough and Tricky questions: Factors.

If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

(A) 2
(B) 3
(C) 6
(D) 8
(E) 10

Let say p = 10, checking divisibility by 80

$$\frac{10 * 10 * 10}{80} = \frac{25}{2}$$

Numerator falling short of 2

So, lets say p = 20, again checking divisibility by 80

$$\frac{20*20*20}{80} = 100$$

20 is the least value of p for which $$p^3$$ can be completely divided by 80

There are 6 distinct factors of 20 >> 1, 2, 4, 5, 10, 20

One more way:

$$20 = 2^2 * 5^1$$

Distinct factors = (2+1)*(1+1) = 3*2 = 6
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Factors and Divisibility  [#permalink]

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If p3 is divisible by 80, then the positive integer p must have at least how many distinct factors?
(A) 2 (B) 3 (C) 6 (D) 8 (E) 10

Please someone explain this question with solution .Thanks
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Posts: 7987
If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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abhisheknandy08 wrote:
If p3 is divisible by 80, then the positive integer p must have at least how many distinct factors?
(A) 2 (B) 3 (C) 6 (D) 8 (E) 10

Please someone explain this question with solution .Thanks

hi,
the method to find distinct factors is..
step 1.. break down the integer in its basic form with prime numbers.. 80=2^4*5...
step 2.. formula is$$a^x*b^y... (x+1)(y+1)$$... so here the answer will be (4+1)(1+1)=5*2=10
ans E..
hope it helped

but it seems you mean p3 as $$p^3$$...
so p^3 will have atleast$$2^4*5$$as its factor,
and therefore, p will have atleast $$2^2*5$$ as factors..
ans 3*2=6 ans C
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Re: Factors and Divisibility  [#permalink]

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abhisheknandy08 wrote:
If p3 is divisible by 80, then the positive integer p must have at least how many distinct factors?
(A) 2 (B) 3 (C) 6 (D) 8 (E) 10

Please someone explain this question with solution .Thanks

Since p is an Integer, therefore p^3 must a perfect cube

Perfect Cube is a number that has all the powers of its Prime factors a multiple of 3 when the Number is written in Prime factorized form

But $$p^3 = 80x = 2^4*5*x$$

i.e. The value of $$x$$ must be a smallest number which can make p^3 a Perfect cube and keep the number smallest for Minimum number of factors of p

i.e. $$x_{min} = 2^2*5^2$$

such that $$(p^3)_{min} = 2^4*5*2^2*5^2 = 2^6*5^3$$

i.e. $$p_{min} = 2^2*5$$

Number of Factors of $$2^2*5 = (2+1)*(1+1) = 3*2 = 6$$

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Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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VeritasPrepKarishma wrote:
ggarr wrote:
If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

2
3
6
8
10

Prime factorize $$80 = 2^4 * 5$$
If $$p^3$$ has at least four 2s and a 5, it must have at least six 2s and three 5s (Every prime factor of $$p^3$$ must have a power which is a multiple of 3).
So p must have at least two 2s and a 5 as factors.

Minimum value of $$p = 2^2 * 5$$
This gives us $$(2+1)*(1+1) = 6$$ distinct factors (at least)

I fail to understand what you mean by "every prime factor of p must have a power which is a multiple of 3".
My guess is that as there are 3 p's, they must all have the same factors with powers and hence 2^4 and 5, have been considered as 2^6 and 5^3. so it can be evenly divided between 3 p's and their total of 8000 is divisible by P. Could you shared some light on the same.
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Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Bunuel wrote:

Tough and Tricky questions: Factors.

If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

(A) 2
(B) 3
(C) 6
(D) 8
(E) 10

80 = $$2^4$$ x $$5^1$$

Since p^3 is divisible by $$2^4$$ x $$5^1$$ the least value of p will be $$2^6$$ x $$5^3$$ ; where $$p$$ = $$5^1$$ x $$2^2$$

So, p must have (1+1) ( 2 + 1 ) => 6 factors, answer will be (C)

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Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Bunuel wrote:

Tough and Tricky questions: Factors.

If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

(A) 2
(B) 3
(C) 6
(D) 8
(E) 10

$$p^3$$ = 80m, where m is any integer.

Now here key point is that 80m is a perfect cube. [ We know this because it is given that p is a positive integer]

Now the question says "at least".

let us see how 80m can be a perfect cube.

80m = 8 * 2 *5 *m = $$2^3$$ * 2 * 5 * m

So we need to multiply "2" by $$2^2$$, so that we get $$2^3$$
We also need to multiply "5" by $$5^2$$, so that we get $$5^3$$

so m is $$2^2$$ * $$5^2$$

With above value of m, p becomes (at least) 2*2*5 = $$2^2$$ * 5

Distinct factors (Power of First term +1) (Power of Second term +1) [ You need to know this formula]

(2+1)(1+1) = 6

C is the answer.
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Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Let's start by breaking 80 down into its prime factorization: 80 = 2 × 2 × 2 × 2 × 5. If p^3 is divisible by 80, p^3 must have 2, 2, 2, 2, and 5 in its prime factorization. Since p^3 is actually p × p × p, we can conclude that the prime factorization of p × p × p must include 2, 2, 2, 2, and 5.

Let's assign the prime factors to our p's. Since we have a 5 on our list of prime factors, we can give the 5 to one of our p's:

p: 5
p:
p:

Since we have four 2's on our list, we can give each p a 2:

p: 5 × 2
p: 2
p: 2

But notice that we still have one 2 leftover. This 2 must be assigned to one of the p's:

p: 5 × 2 × 2
p: 2
p: 2

We must keep in mind that each p is equal in value to any other p. Therefore, all the p's must have exactly the same prime factorization (i.e. if one p has 5 as a prime factor, all p's must have 5 as a prime factor). We must add a 5 and a 2 to the 2nd and 3rd p's:

p: 5 × 2 × 2 = 20
p: 5 × 2 × 2 = 20
p: 5 × 2 × 2 = 20

We conclude that p must be at least 20 for p^3 to be divisible by 80. So, let's count how many factors 20, or p, has:

1 × 20
2 × 10
4 × 5

20 has 6 factors. If p must be at least 20, p has at least 6 distinct factors.

The correct answer is C.
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Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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VeritasPrepKarishma wrote:
ggarr wrote:
If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

2
3
6
8
10

Prime factorize $$80 = 2^4 * 5$$
If $$p^3$$ has at least four 2s and a 5, it must have at least six 2s and three 5s (Every prime factor of $$p^3$$ must have a power which is a multiple of 3).
So p must have at least two 2s and a 5 as factors.

Minimum value of $$p = 2^2 * 5$$
This gives us $$(2+1)*(1+1) = 6$$ distinct factors (at least)

Quote:
Can you explain the line in the bracket
(Every prime factor of p^3 must have a power which is a multiple of 3)

Take any positive integer N.

Say $$N = 6 = 2*3$$

$$N^3 = 6^3 = (2^3 * 3^3)$$

Say $$N = 18 = 2 * 3^2$$

$$N^3 = 18^3 = (2^3 * 3^6)$$

Similarly, since p is a positive integer, it will be made up of some prime factors. When you cube it, every prime factor of p^3 will have a power of 3 or a multiple of 3.
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If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Bunuel wrote:

Tough and Tricky questions: Factors.

If $$p^3$$ is divisible by 80, then the positive integer p must have at least how many distinct factors?

(A) 2
(B) 3
(C) 6
(D) 8
(E) 10

OFFICIAL SOLUTION

The prime factorization of 80 is (2)(2)(2)(2)(5) = 2^4*5^1. Thus, $$p^3 = 2^4*5^1*x$$, where x is some integer.

Assigning the factors of p 3 to the prime boxes of p will help us see what the factors of p could be.

The prime factors in ( ) above are factors not explicitly given for $$p^3$$, but which must exist. We know that $$p^3$$ is the cube of an integer, and must have “triples” of the prime factors of p. Since $$p^3$$ has a factor of $$2^3$$, p must have a factor of 2. The fact that $$p^3$$ has an “extra” 2 and a 5 among its factors indicates that p has additional factors of 2 and 5.

If p is a multiple of (2)(2)(5) = 20, then at the very least p has 1, 2, 4, 5, 10, and 20 as factors. So we can conclude that p has at least 6 distinct factors.

Alternatively, we can use this shortcut for computing the number of factors:
(2’s exponent + 1)(5’s exponent + 1) = (2 + 1)(1 + 1) = (3)(2) = 6.

The correct answer is C.
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Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Quote:

If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

(A) 2
(B) 3
(C) 6
(D) 8
(E) 10

Since p^3/80 = integer, we can say that the product of 80 and some integer n is equal to a perfect cube. In other words, 80n = p^3.

We must remember that all perfect cubes break down to unique prime factors, each of which has an exponent that is a multiple of 3. So let’s break down 80 into primes to help determine what extra prime factors we need to make 80n a perfect cube.

80 = 10 x 8 = 5 x 2 x 2 x 2 x 2 = 5^1 x 2^4

In order to make 80n a perfect cube, we need two more 2s, and two more 5s. Thus, the smallest perfect cube that is a multiple of 80 is 2^6 x 5^3.

To determine the least possible value of p, we can take the cube root of 2^6 x 5^3 and we have:

2^2 x 5^1

To determine the total number of factors, we add 1 to each exponent attached to each base and multiply those values together.

(2 + 1)(1 + 1) = 3 x 2 = 6 total factors.

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GMAT 1: 580 Q36 V32 GMAT 2: 660 Q39 V41 GRE 1: Q159 V160 Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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VeritasPrepKarishma wrote:
ggarr wrote:
If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

2
3
6
8
10

(Every prime factor of $$p^3$$ must have a power which is a multiple of 3).
So p must have at least two 2s and a 5 as factors.

SO why isn't it 2^12?
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Re: If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Bunuel wrote:

Tough and Tricky questions: Factors.

If p^3 is divisible by 80, then the positive integer p must have at least how many distinct factors?

(A) 2
(B) 3
(C) 6
(D) 8
(E) 10

SOLUTION
p^3 divisible by 80

p^3 => factorising 80and writing in below format x=2 and y = 5 makes cube and then p= 2x2x5=20
2-2-2
2-x-x
5-y-y

20= 2^2 . 5^1
total factors = (2+1) ( 1+1) = 3x2= 6

Option C
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If p^3 is divisible by 80, then the positive integer p must have at le  [#permalink]

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Given $$P^3$$ divisible by 80
=> $$P^3$$ = $$2^4 * 5 * m$$ (where m is any integer)
=> to make P as integer, min value of m = $$2^2 * 5^2$$
=> min value of $$P^3$$ = $$2^4 * 5 * 2^2 * 5^2$$
=> min value of P = $$2^2 * 5$$
mininum number of factors of P = (2+1)(1+1) = 6 => (C)
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