Prime challenge

Number Theory Level pending

Given are five different prime numbers A , B , C , D A, B, C, D and E E that satisfy the following conditions

A + B + D = E A + B + D = E

3 × B < E + 10 3 \times B < E + 10

C + B = A C + B = A

2 × A + C = E 1 2 \times A + C = E - 1

What is the value of E E ?

29 19 113 479 43

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1 solution

As the given prime numbers are all different, the first condition implies that A , B , D , E A, B, D, E are all odd. The third condition then implies that C C is even, i.e. C = 2 C=2 .

Using C = 2 C=2 and A = B + 2 A=B+2 we can eliminate A A and C C and are left with the following three conditions:

2 × B + D + 2 = E 2 \times B + D + 2 = E

2 × B + 7 = E 2 \times B + 7 =E

3 × B 10 < E 3 \times B - 10 < E

The first two conditions imply D = 5 D = 5 . The second two conditions imply B < 17 B < 17 . Taking into account that A = B + 2 A= B + 2 also needs to be a prime number and A A and B B need to be different to D = 5 D=5 we can conclude B = 11 B=11 and hence A = 13 A=13 and E = 29 E=29 .

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