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Re: If the number of different positive factors of (2^y)(3^3) is the same [#permalink]
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Awli wrote:
If the number of different positive factors of (2^y)(3^3) is the same as the number of different factors of (2^51), what is the value of y?

a) 11

b) 12

c) 13

d) 48

e) 51


Finding the Number of Factors of an Integer

First make prime factorization of an integer \(n=a^p*b^q*c^r\), where \(a\), \(b\), and \(c\) are prime factors of \(n\) and \(p\), \(q\), and \(r\) are their powers.

The number of factors of \(n\) will be expressed by the formula \((p+1)(q+1)(r+1)\). NOTE: this will include 1 and n itself.

Example: Finding the number of all factors of 450: \(450=2^1*3^2*5^2\)

Total number of factors of 450 including 1 and 450 itself is \((1+1)*(2+1)*(2+1)=2*3*3=18\) factors.

According to the above, the number of factors o f (2^y)(3^3) is (y + 1)(3 + 1) = 4y +4 and the number of factors of 2^51 is 51 + 1 = 52. Thus given that 4y +4 = 52 --> y = 12.

Answer: B.

Hope it's clear.
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Re: If the number of different positive factors of (2^y)(3^3) is the same [#permalink]
Lucky2783 wrote:
Awli wrote:
If the number of different positive factors of (2^y)(3^3) is the same as the number of different factors of (2^51), what is the value of y?

a) 11

b) 12

c) 13

d) 48

e) 51


Number of factors of \(N= a^x * b^y\) where 'a' and 'b' are prime factors of N is

(X+1) (y+1)


So 4 (y+1)=52
y=12



Why 4 (y+1) ??

Thanks
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Re: If the number of different positive factors of (2^y)(3^3) is the same [#permalink]
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