Question

If 21y5 is a multiple of 9, where y is a digit. What is the value of y

Answer 1

if a number is divisible by any number then it is multiple of the number

divisiblity rule of 9 is sum of digits must be divisible by 9

2+1+y+5 is divisble by 9

11+y is divisible by 9

therefore his 7