Maths Olympiad Prep

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Number theory Difficulty 6.6 National olympiad Find the answer

Let a a , b b , c c , d d , (a+b+c+18+d) (a + b + c + 18 + d) , (a+b+c+18d) (a + b + c + 18 - d) , (b+c) (b + c) , and (c+d) (c + d) be distinct prime numbers such that a+b+c=2010 a + b + c = 2010 , a a , b b , c c , d3 d \neq 3 , and d50 d \le 50 . Find the maximum value of the difference between two of these prime numbers.

A number or a short expression. Spacing and $ signs are ignored.

Solution

1. We are given that a,b,c,d,(a+b+c+18+d),(a+b+c+18d),(b+c),a, b, c, d, (a + b + c + 18 + d), (a + b + c + 18 - d), (b + c), and (c+d)(c + d) are distinct prime numbers, and a+b+c=2010a + b + c = 2010. Additionally, a,b,c,d3a, b, c, d \neq 3 and d50d \leq 50.

2. From the conditions, we have:
a+b+c+18+d=2028+d(prime number) a + b + c + 18 + d = 2028 + d \quad \text{(prime number)}
a+b+c+18d=2028d(prime number) a + b + c + 18 - d = 2028 - d \quad \text{(prime number)}
Since both 2028+d2028 + d and 2028d2028 - d must be prime, dd must be odd (as adding or subtracting an even number from an even number results in an even number, which cannot be prime except for 2, but d3d \neq 3).

3. Next, consider c+dc + d. Since c+dc + d is a prime number greater than 2, it must be odd. Therefore, cc must be even. The only even prime number is 2, so c=2c = 2.

4. Substituting c=2c = 2 into a+b+c=2010a + b + c = 2010, we get:
a+b+2=2010    a+b=2008 a + b + 2 = 2010 \implies a + b = 2008

5. Now, we need to ensure that 2028+d2028 + d and 2028d2028 - d are prime numbers. Additionally, d50d \leq 50 and dd must be such that both 2028+d2028 + d and 2028d2028 - d are primes.

6. We also need to ensure that dd and d+2d + 2 are both primes. The possible values of dd that satisfy these conditions are d{5,11,29,41}d \in \{5, 11, 29, 41\}.

7. Checking these values:
- For d=5d = 5:
2028+5=2033(not prime) 2028 + 5 = 2033 \quad (\text{not prime})
20285=2023(prime) 2028 - 5 = 2023 \quad (\text{prime})
- For d=11d = 11:
2028+11=2039(prime) 2028 + 11 = 2039 \quad (\text{prime})
202811=2017(prime) 2028 - 11 = 2017 \quad (\text{prime})
- For d=29d = 29:
2028+29=2057(prime) 2028 + 29 = 2057 \quad (\text{prime})
202829=1999(prime) 2028 - 29 = 1999 \quad (\text{prime})
- For d=41d = 41:
2028+41=2069(prime) 2028 + 41 = 2069 \quad (\text{prime})
202841=1987(prime) 2028 - 41 = 1987 \quad (\text{prime})

8. Among these values, d=41d = 41 gives the highest value for 2028+d2028 + d. Therefore, the maximum value of the difference between two of these prime numbers is:
(a+b+c+18+d)c=(2028+d)2=2026+d (a + b + c + 18 + d) - c = (2028 + d) - 2 = 2026 + d
Substituting d=41d = 41:
2026+41=2067 2026 + 41 = 2067

The final answer is 2067\boxed{2067}

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.