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# If s@t= (1/s) + (1/t) and s and t are prime numbers, does

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Joined: 05 Apr 2008
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If s@t= (1/s) + (1/t) and s and t are prime numbers, does [#permalink]

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10 Sep 2008, 07:43
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If s@t= (1/s) + (1/t) and s and t are prime numbers, does s@t=1?

1. s+t different than 4
2. (s/t) is different than 1

a) 1 is sufficient
b) 2 is sufficient
c) 1 & 2 together are sufficient
d) Either 1 or 2 is sufficient
e) Neither 1 nor 2 is sufficient

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SVP
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Re: Math Question - Data Sufficiency [#permalink]

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10 Sep 2008, 07:58
HVD1975 wrote:
If s@t= (1/s) + (1/t) and s and t are prime numbers, does s@t=1?

1. s+t different than 4
2. (s/t) is different than 1

a) 1 is sufficient
b) 2 is sufficient
c) 1 & 2 together are sufficient
d) Either 1 or 2 is sufficient
e) Neither 1 nor 2 is sufficient

D
(1/s) + (1/t) = 1 is possible only when s=2 and t=2
1) s+t different than 4
then 1/s+1/t must be fraction.
so does s@t=1? Ans No.

Sufficient.
2) same logic as above.

sufficient
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Re: Math Question - Data Sufficiency [#permalink]

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10 Sep 2008, 14:52
D

s@t = (1/s) + (1/t)
s and t are prime nos
They never told s and t are different

for s@t = 1 ==> (1/s) + (1/t) = 1
s and t have to be equal to 2
so that 1/2 + 1/2 = 1, No two prime numbers will give s@t = 1

(a) s+t different than 4
so s+t can be 5,6,7....
so s and t can be 2,3 or 3,4 or 3,3....
subsitute the value of s and t in s@t = 1/s + 1/t is not equal to 1

so A alone is sufficent to answer the question

(b) (s/t) if different than 1
which means s and t cannot be the same.
subsitute the val;ue of s ant with any two prime number...s@t = 1/s+1/t is not equal to 1

so B alone is sufficent to answer the question

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Re: Math Question - Data Sufficiency   [#permalink] 10 Sep 2008, 14:52
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