Question:
Find the value of z for which the number 471z8 is divisible by 9. Also, find the number.
Solution:
If a number is divisible by 9 , then the sum of the digits is also divisible by 9 .
Sum of the digits of the given number $=4+7+1+z+8=20+z$
$20+z=27$, for $z=7$
27 is divisible by 9 .
Therefore, $471 z 8$ is divisible by 9 if $z$ is equal to 7 .
The number is 47178 .