# Happy Birthday Kostya!

**Discrete Mathematics**Level 2

*Today is my friend Kostya's birthday, and this is my problem in his honour.*

Andrei and Kostya sit in different rooms. Andrei writes a number from 1 to 8, inclusive, on a piece of paper. Kostya, with no knowledge of Andrei's number, also writes a number from 1 to 8 on *his* piece of paper. When both numbers have been written, the two pieces of paper are connected to form a two-digit number: Andrei's number goes first, Kostya's second. What is the probability that \(\overline{ab}\) is divisible by 9?

**Details and Assumptions:**

Both numbers can be the same.

Express your answer as a decimal.

There are a total of 8 numbers to choose from.

**Your answer seems reasonable.**Find out if you're right!

**That seems reasonable.**Find out if you're right!

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