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Lê Quốc Trần Anh Coordinator

22/03/2018 at 11:35
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When three consecutive positive integers are multiplied, the product is 16 times the sum of the three integers. What is the difference of the product minus the sum?




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    ¤« 24/03/2018 at 13:10

    Let n – 1, n and n + 1 be positive consecutive integers such that (n – 1) ×n × (n + 1) = 16 × [(n – 1) + n + (n + 1)]. Simplifying and solving for n, we have n(n2 – 1) = 16 × 3n → n3 – n = 48n → n3 – 49n = 0

    => n(n2 – 49) = 0. So, n = 0 or n2 − 49 = 0 → (n + 7)(n – 7) = 0 => n = −7 or n = 7. Since n is a positive integer, it follows that the three consecutive numbers are 6, 7 and 8. The difference between their product and sum is 6 × 7 × 8 – (6 + 7 + 8) = 336 – 21 = 315.

  • ...
    Lê Anh Duy 22/03/2018 at 15:44

     Let n – 1, n and n + 1 be positive consecutive integers such that (n – 1) ×n × (n + 1) = 16 × [(n – 1) + n + (n + 1)]. Simplifying and solving for n, we have n(n2 – 1) = 16 × 3n → n3 – n = 48n → n3 – 49n = 0

    => n(n2 – 49) = 0. So, n = 0 or n2 − 49 = 0 → (n + 7)(n – 7) = 0 => n = −7 or n = 7. Since n is a positive integer, it follows that the three consecutive numbers are 6, 7 and 8. The difference between their product and sum is 6 × 7 × 8 – (6 + 7 + 8) = 336 – 21 = 315. 


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