Exercise16.2
Question 1
If 21y5 is a multiple of 9, where y is a digit, what is the value of y?
Answer:
Solution:
If a number is a multiple of 9, then the sum of its digits will be divisible by 9.
Sum of the digits of
21 5 2 1 5 8 y y y
Hence,
should be a multiple of 9.
This is possible when
is any one of these numbers 0, 9, 18, 27, and so on …
However, since y is a single digit number, this sum can be 9 only.
So, y should be 1 only.
Question 2
If 31z5 is a multiple of 9, where z is a digit, what is the value of z?
You will find that there are two possible values of z. Why is this so?
Answer:
Solution:
If a number is a multiple of 9, then the sum of its digits will be divisible by 9.
Sum of the digits of
31 5 3 1 5 9 z z z
Hence,
should be a multiple of 9.
This is possible when
is any one of these numbers 0, 9, 18, 27, and so on …
However, since z is a single digit number, this sum can be either 9 or 18. So, z should
be either 0 or 9.
Question 3
If 24xis a multiple of 3, where x is a digit, what is the value of x?
Answer:
Solution:
Since 24x is a multiple of 3, the sum of its digits is a multiple of 3.
Sum of the digits of
Hence,
is a multiple of 3.
This is possible when
is any one of these numbers 0, 3, 6, 9, and so on …
Since x is a single digit number, the sum of the digits can be 6 or 9 or 12 or 15 and