MP Board Class 8th Maths Solutions Chapter 16 Playing with Numbers Ex 16.2

MP Board Class 8th Maths Solutions Chapter 16 Playing with Numbers Ex 16.2

MP Board Class 8th Maths Solutions Chapter 16 Playing with Numbers Ex 16.2

Question 1.
If 21y5 is a multiple of 9, where y is a digit, what is the value of y?
Solution:
The given number is 21y5
For this number to be multiple of 9, the sum of its digits should be a multiple of 9.
∴ 2 + 1 + y + 5 is a multiple of 9.
or 8 + y is a multiple of 9.
For y to be a single digit number,
8 + y = 9 ⇒ y = 1

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 answers for the last problem. Why is this so?
Solution:
The given number is 31z5.
For this number to be multiple of 9, the sum of its digits should be a multiple of 9.
∴ 3 + 1 + z + 5 is a multiple of 9.
or z + 9 is a multiple of 9.
∴ For z to be a single digit number,
z + 9 = 9 or z + 9 = 18
⇒ z = 0 or z = 9
Hence, z = 0, 9
We get two answers, because 9 and 18, both are multiples of 9.

Question 3.
If 24x is a multiple of 3, where x is a digit, what is the value of x? (Since 24x is a multiple of 3, its sum of digits 6 + x is a multiple of 3; so 6 + x is one of these numbers :0, 3, 6, 9, 12, 15, 18, But since x is a digit, it can only be that 6 + x = 6 or 9 o r12 or 15. Therefore, x = 0 or 3 or 6 or 9. Thus, x can have any of four different values).
Solution:
The given number 24x is a multiple of 3.
⇒ Sum of the digits of this number are also a multiple of 3.
∴ 2 + 4 + x = x + 6 is a multiple of 3.
For x to be a single digit number,
x + 6 = 6, 9, 12, 15 or x = 0, 3, 6, 9.

Question 4.
If 31z5 is a multiple of 3, where z is a digit, what might be the values of z?
Solution:
As the given number 31z5 is a multiple of 3, the sum of its digits should also be a multiple of 3.
∴ 3 + 1 + z + 5 is a multiple of 3.
or z + 9 is a multiple of 3.
Now, for z to be a single digit number,
z + 9 = 9, 12, 15, 18 or z = 0, 3, 6, 9

MP Board Class 8th Maths Solutions