Selina Concise Class 8 Math Chapter 5 Playing with Numbers Exercise 5C Solutions
EXERCISE 5C
(1) A number is divisible by 2, if its unit digit is zero or an even number.
Therefore, (i) and (ii) is divisible by 2.
(2) A number is divisible by 3, if sum of its digit id divisible by 3.
(i) 2 + 6 + 1 = 9, which is divisible by 3.
(ii) 7 + 7 + 7 = 21, which is divisible by 3.
(iii) 6 + 6 + 5 + 7 = 24, which is divisible by 3.
(iv) 2 + 5 + 7 + 4 = 20, which is not divisible by 3.
(3) A number is divisible by 4, if the two digit number formed by its ten’s digit and unit digit is divisible by 4.
(i) 60 is divisible by 4
∴ 360 is divisible by 4
(ii) 80 is divisible by 4
∴ 3180 is divisible by 4
(iii) 48 is divisible by 4
∴ 5348 is divisible by 4
(iv) 56 is divisible by 4
∴ 7756 is divisible by 4
(4) A number is divisible by 5, if its unit digit is 0 or 5.
Here, (i) and (iii) are divisible by 5.
(5) A number is divisible by 10, if its unit digit is zero.
Therefore, (i) and (iii) are divisible by 10.
(6) A number is divisible by 11, if the difference between the sum of its digits in even places and the sum of its digit in odd places is either 0 or divisible by 11.
(i) Counting from the right hand side, the sum of its digits in odd places = 3 + 5 = 8
And, the sum of its digits in even places = 2 + 6 = 8
The difference between those two sums = 8 – 8 = 0
∴ 2563 is divisible by 11.
(ii) Counting from the right hand side, the sum of its digits in odd places = 3 + 7 = 10
And, the sum of its digits in even places = 8 + 0 = 8
The difference between those two sums = 10 – 8 = 2
∴ 2563 is not divisible by 11.
(iii) Counting from the right hand side, the sum of its digits in odd places = 5 + 6 + 9 = 20
And, the sum of its digits in even places = 3 + 5 = 8
The difference between those two sums = 20 – 8 = 12
∴ 2563 is not divisible by 11.
