Q10. 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.

Answers (1)

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

 

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