Question

lf 21y5is a multiple of 9 where y is adigit; what is the value of y with method

Answer 1

Divisibility rule for 9 is : number should be a multiple of 3

Divisibility rule of 3 is : sum of digits of a number should be divisible by 3

so, 2+1+y+5=8+y (when y=1, then sum=8+1=9 i.e 9 is divisible by 3)

Hence, y=1 (answer)