Question

10. If 21y 5 is a multiple of 9, where y is a digit, what is the value of y?​

Answer 1

Given:  21y5 is a multiple of 9, where y is a digit.

To find: what is the value of y?​

Solution:

• Now we know the divisibility test of 9 which is:

• If a number is divisible by nine, then the sum of the digits must be divisible by nine.

• So, we have:

                   2 + 1 + y + 5 = 9

                   8 + y = 9

                   y = 9 - 8

                   y = 1.

• Verifying it, we get:

                   2115 / 9 = 235, so y = 1 is true.

Answer:

            So the value of y is 1.