Class 8 Maths

Square Root

Exercise 6.1

Question 1: What will be the unit digit of the squares of the following numbers?

(i) 81

Answer: 1
Explanation Since, 12 ends up having 1 as the digit at unit’s place so 812 will have 1 at unit’s place.

(ii) 272

Answer: 4
Explanation: Since, 22 = 4, therefore, square of 272 will have 2 at it's unit place.
So, 2722 will have 4 at unit’s place

(iii) 799

Answer: 1
Explanation: Since, 92 = 81, So, 7992 will have 1 at unit’s place

(iv) 3853

Answer: 9
Explanation: Since 32 = 9, so, 38532 will have 9 at unit’s place.

(v) 1234

Answer: 6
Explanation: Since, 42 = 16, so, 12342 will have 6 at unit’s place


(vi) 26387

Answer: 9.
Explanation: Since, 72 = 49. Therefore, 263872 will have 9 at unit’s place

(vii) 52698

Answer: 4
Explanation: Since, 82 = 64. So, 526982 will have 4 at unit’s place

(viii) 99880

Answer: 0
Explanation: Since, 02 = 0. So, 998802 will have 0 at unit’s place

(ix) 12796

Answer: 6
Explanation: Since, 62 = 36. So, 127962 will have 6 at unit’s place

(x) 55555

Answer: 5
Explanation: Since, 52 = 25, therefore, 555552 will have 5 at unit’s place

Question 2: The following numbers are obviously not perfect squares. Give reason.

(i) 1057 (ii) 23453 (iii) 7928 (iv) 222222 (v) 64000 (vi) 89722 (vii) 222000 (viii) 505050

Answer: (i), (ii), (iii), (iv), (vi) don’t have any of the 0, 1, 4, 5, 6, or 9 at unit’s place, so they are not be perfect squares.
(v), (vii) and (viii) don’t have even number of zeroes at the end so they are not perfect squares.

Question 3: The squares of which of the following would be odd numbers?

(i) 431 (ii) 2826 (iii) 7779 (iv) 82004

Answer: (i) 431 and (iii) 779.
Explanation: (i) and (ii) have odd numbers as their square, because an odd number multiplied by another odd number always results in an odd number.

Question 4: Observe the following pattern and find the missing digits.
112 = 121
1012 = 10201
10012 = 1002001
1000012 = 1.........2.......1
100000012 = ...............

Answer: 1000012 = 10000200001
100000012 = 100000020000001
Explanation: Start with 1 followed as many zeroes as there are between the first and the last one, followed by two again followed by as many zeroes and end with 1.


Question 5: Observe the following pattern and supply the missing numbers.
112 = 121
1012 = 10201
101012 = 102030201
10101012 = ..................
..............2 =10203040504030201

Answer: 10101012 = 1020304030201
1010101012 =10203040504030201
Explanation: Start with 1 followed by a zero and go up to as many number as there are number of 1s given, follow the same pattern in reverse order.

Question 6: Using the given pattern, find the missing numbers.

12 + 22 + 22 = 32
22 + 32 + 62 = 72
32 + 42 + 122 = 132
42 + 52 + _2 = 212
52 + _2 + 302 = 312
62 + 72 + _2 = _2

Answer: 42 + 52 + 202 = 212
52 + 62 + 302 = 312
62 + 72 + 422 = 432
Relation among first, second and third number - Third number is the product of first and second number
Relation between third and fourth number - Fourth number is 1 more than the third number

Question 7: Without adding, find the sum.

(i) 1 + 3 + 5 + 7 + 9

Answer: Since, there are 5 consecutive odd numbers, Thus, their sum = 52 = 25

(ii) 1 + 3 + 5 + 7 + 9 + I1 + 13 + 15 + 17 +19

Answer: Since, there are 10 consecutive odd numbers, Thus, their sum = 102 = 100

(iii) 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 + 21 + 23

Answer: Since, there are 12 consecutive odd numbers, Thus, their sum = 122 = 144
Explanation: 1 + 3 = 22 = 4
1 + 3 + 5 = 32 = 9
1 + 3 + 5 + 7 = 42 =16
1 + 3 + 5 + 7 + 9 = 52 = 25
In other words this is a way of finding the sum of n odd numbers starting from 1.
Therefore, Sum of n odd numbers starting from 1 = n2


Question 8: (i) Express 49 as the sum of 7 odd numbers.

Answer: Since, 49 = 72
So, 72 can be expressed as follows:
1 + 3 + 5 + 7 + 9 + 11 + 13

(ii) Express 121 as the sum of 11 odd numbers.

Answer: Since, 121 = 112
Therefore, 121 = 1 + 3 + 5 + 7 + 9 + 11 + 13 + 15 + 17 + 19 + 21

Question 9: How many numbers lie between squares of the following numbers?

(i) 12 and 13

Answer: 122 = 144
132 = 169
Now, 169 - 144 = 25
So, there are 25 - 1 = 24 numbers lying between 122 and 132

(ii) 25 and 26

Answer: We know that, 252 = 625
And, 262 = 676
Now, 676 - 625 = 51
So, there are 51 - 1 = 50 numbers lying between 252 and 262

(iii) 99 and 100

Answer: We know that, 992 = 9801
And, 1002 = 10000
Now, 10000 - 9801 = 199
So, there are 199 - 1 = 198 numbers lying between 992 and 1002


Ex 6.1

Ex 6.2

Ex 6.3

Ex 6.4