Franklin thinks of the sum , where and are positive integers satisfying . Calvin comes to help him out. Assuming Calvin is always correct in his solutions to every math problem, what will be his answer?
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Let G = g cd ( a , b ) and L = lcm ( a , b ) . Then we have:
g cd ( a , b ) + lcm ( a , b ) + a b G + L + G L G L + G + L + 1 ( G + 1 ) ( L + 1 ) = 2 0 1 4 = 2 0 1 4 = 2 0 1 5 = 2 0 1 5 Note that g cd ( a , b ) × lcm ( a , b ) = a b and that 2 0 1 5 = 5 × 1 3 × 3 1
Since G ≤ L , the possible values of G and L are ⎩ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎧ 1 × 2 0 1 5 = 2 0 1 5 5 × 4 0 3 = 2 0 1 5 1 3 × 1 5 5 = 2 0 1 5 3 1 × 6 5 = 2 0 1 5 ⟹ G = 0 ⟹ G = 4 ⟹ G = 1 2 ⟹ G = 3 0 L = 2 0 1 4 L = 4 0 2 L = 1 5 4 L = 6 4
We note that ( G , L ) = ( 0 , 2 0 1 4 ) is unacceptable. Since G 2 ∣ a b , we have G 2 ∣ G L ⟹ G ∣ L . We note that none of the remaining three L 's us divisible by the respective G 's. Come on Frank! There is no a and b that satisfy this!