Activity : Ask all the students in your class to write a 3-digit number. Choose any student from the room at random. What is the probability that the number written by her/him is divisible by 3? Remember that a number is divisible by 3, if the sum of its digits is divisible by 3.

Given 3- digit numbers = 100, 101, 102 … 999 and total number of 3-digit numbers = 999 – 99 = 900
Numbers divisible by 3 = 102, 105, 108 … 999. So, the number of numbers divisible by 3 = 300
Therefore,
P(number divisible by 3) = 300/900 = 1/3
Hence, the probability that the number written by her/him is divisible by 3 is 1/3.