MathDB

Problem 3

Part of 2016 Nigerian Senior MO Round 2

Problems(1)

Sums and probability

Source: 2016 Nigerian Senior MO Round 2

11/16/2022
The integers 1,2,…,91, 2, \dots , 9 are written on individual slips of paper and all are put into a bag. Ade chooses a slip at random, notes the integer on it, and replaces it in the bag. Bala then picks a slip at random and notes the integer written on it. Chioma then adds up Ade's and Bala's numbers. What is the probability that the unit's digit of this sum is less that 55?
combinatoricsprobability