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Let a, b and c be the length of sides of a triangle ABC such that 9 a c 8 c b 7 b a + = + = + . If r and R are the radius of incircle and radius of circumcircle of the triangle ABC, respectively, then the value of r R is equal to :

1. 2 5
2. 2
3. 2 3
4. 1

Correct answer: 2 5

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