Task# Multiples of nine

Illustrative MathematicsVaries

This task examines the interesting fact that when a number is divisible by 9 then the sum of its digits is also divisible by 9. Only one and two digit numbers are examined here. A natural extension of this activity would be to see if this pattern remains true for three digit or larger numbers. At this age, students are multiplying large numbers by a single digit number and so they could be encouraged to pursue further this interesting fact about the sum of the digits in numbers divisible by 9.