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# If s@t= 1/s + 1/t where both s and t are prime numbers, s@t

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If s@t= 1/s + 1/t where both s and t are prime numbers, s@t [#permalink]

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01 Nov 2004, 18:03
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If s@t= 1/s + 1/t where both s and t are prime numbers, s@t = 1?

1. s+t not equal to 4

2. s/t is not equal to 1

Pls explain
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01 Nov 2004, 19:12
D it is
Expression can also be written as [s+t] / st
Only way expression can be = 1 is if both s and t = 2
1) s+t not equal to 4 so therefore, expression cannot be equal to 1. sufficient
2) says that s and t are different primes. Since we need s and t = 2, we know that different primes will NOT yield 1 as final answer. sufficient
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Best Regards,

Paul

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