If 21y5 is a multiple of 9, where y is a digit, what is the value of y?

Since 21y5 is a multiple of 9.
Therefore according to the divisibility rule of 9, the sum of all the digits should be a
multiple of 9.
∴ 2+1+y+5=8+y ⇒8+y=9 ⇒y=1

Class 8 Maths Chapter 11 Exercise 16.2 Solution in Video

for more answers vist to:
https://www.tiwariacademy.com/ncert-solutions/class-8/maths/chapter-16/