IIT JEE , AIEEE Forum - Mathematics , Algebra

mukundmadhav

What I do is, consider A.Ps of common differences 1 through 7
For 7, only one solution
For 6, 3 solutions
For 5, 5 solutions
For 4, 7 solutions
For 3, 9 solutions
For 2, 11 solutions
For 1, 13 solutions

So total of 49 favourable outcomes. And a total of 455 outcomes
So answer's 7/65..

But allamraju's method is obviously much better..

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