Question

if 21y5 is a multiple of 9 where y is a digit find the value of v

Answer 1

if a number is multiple of 9, sum of all its digits is a multiple of 9. using same law here 
2+1+y+5=9 or 18 or 27 or so on 
8+y=9 or 18 or 27 or so on 
but y cannot be greater than 9 
hence y=1 is the acceptable answer





hope it is usefu l to you

Answer 2

Since 21y5 if a multiple of 9,

The sum of digits is divisible by 9

Sum of the digits can be 9, 18, 27 etc

But if the sum of digits is 18 or more then the value of y will be more than 9 that is not possible

So, the sum of digits = 9

=> 2 + 1 + y + 5 = 9

=> y + 8 = 9

=> y = 1

Number is 2115

And value of y is 1