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Australian Intermediate Mathematics Olympiad 2023 Question 5

AIMO AUSTRALIA · Australian Intermediate Mathematics Olympiad 2023

Question 5

Arrange $1,2,3,4,5,6$ in a line as the base of a number pyramid. Each number above the base is the sum of the adjacent pair directly below it. The example shown has base $3,6,1,5,4,2$. How many base arrangements produce a top number divisible by $5$?

Question illustration