Happy Birthday Kostya!
Discrete Mathematics
Level
2
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.
by
Andrei Golovanov