10. 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
This activity can be taken as a general problem: Well, we know the divisibility by 3 is when the sum of all the digits is divisible by 3 So, The student will write the number between 100-999 There are 900 3-digit numbers, which are 100, 101, 102, 103, ..., 999. The first 3-digit numbers that are exactly divisible by 3 is 102, 105, ..... 999 total numbers which are divisible by 3 = 300 P(the sum of all the digits is divisible by 3) = 300/900 =1/3 Ans:1/3
