20. which part of waste water treatment plant is used to remove big solid impurities:
(a) sedimentation tank (b) sludge removal tank
(c) bar screens (d) sand removal tank
Answers
Explanation:
Question 1
Find the LCM of 12, 16, 24 and 36?
Answers
12
=
2
×
2
×
3
16
=
2
×
2
×
2
×
2
24
=
2
×
2
×
2
×
3
36
=
2
×
2
×
3
×
3
LCM =
2
×
2
×
2
×
2
×
3
×
3
=
144
Question 2
Find the HCF of 70, 105, 175
Answers
70
=
2
×
5
×
7
105
=
3
×
7
×
5
175
=
5
×
5
×
7
HCF =
5
×
7
=
35
Question 3
What are twin primes? Give four examples
AnswersTwo prime numbers whose difference is 2 are called twin primes.
For example:
3 and 5 are twin primes
5 and 7 are twin primes
Question 4
What is a prime triplet? Give an example.
AnswersA prime triplet is a set of three prime numbers of the form:
(p,p+2,p+6) or (p,p+4,p+6)
Some Examples are (5, 7, 11), (7, 11, 13), (11, 13, 17)
Question 5
Arrange the prime factors of 1350 in descending order.
Answers
1350
=
2
×
3
×
3
×
3
×
5
×
5
Prime factors in descending order
5 > 3 >2
Question 6
Find the LCM of the following numbers:
a. 11 and 4
b. 125 and 5
c. 12 and 16
d. 8, 64
Answersa. 44
b. 125
c. 48
d. 64
Question 7
Express 53 as the sum of three odd primes.
Answers53 = 13 + 17 + 23
or 53 = 7 + 17 + 29
Question 8
In a morning walk, three persons step off together. Their steps measure 80 cm, 85 cm and 90 cm respectively. What is the minimum distance each should walk so that all can cover the same distance in complete steps?
AnswersWe have to find the LCM of 80 cm, 85 cm and 90 cm
LCM =12240 cm
Question 9
Find the least number which when divided by 12, 16 ,24 and 36 leaves a remainder 7 in each case.
AnswersLCM of 12,16,24 and 36 =144
Least Number = 144 + 7 = 151
Question 10
Find the multiples of 11 which is greater than 56 but less than 79
AnswersMultiples of 11 = 11,22,33,44,55,66,77,88
So multiples greater than 56 but less than 79 are 66 and 77
Question 11
Find the HCF of the following numbers:
(a) 11, 44
(b) 35, 42
(c) 128, 60
(d) 81, 63
(e) 36, 180
(f) 1152, 1664
(g) 70, 115, 175
(h) 91, 112, 49
(i) 18, 54, 81
(j) 12, 45, 85
Answers1.
a.
11= 11
44 =11 X 2 X 2
HCF =11
b.
35 = 5 x 7
42 = 7 x 3 x 2
HCF =7
c.
128= 2 x 2 x 2 x 2 x 2 x 2 x 2
60 = 2 x 2 x 3 x 5
HCF =4
d. 81 = 3 x 3 x3 x3
63 = 7 x 3 x 3
HCF =9
e.
36 =2 x 2 x3 x3
180 = 2 x 2 x 5 x 3 x 3
HCF = 12
f.
1152=2 x 2 x 2 x 2 x 2 x 2 x 2 x3 x3
1664=2 x 2 x 2 x 2 x 2 x 2 x 2 x 13
HCF= 128
g.
70 =2 x 5 x 3 x 3
115= 23 x 5
175 = 5 x 5 x7
HCF = 5
h.7
i. 9
j. 1
Question 12
Find the LCM of the following numbers:
(a) 4,7,12,84
(b) 25,15,36
(c) 24,36,40
(d) 27,36
(e) 4,8,18
(f) 2,3,4,5,6,7
Answersa.
4
=
2
×
2
7
=
7
×
1
12
=
2
×
2
×
3
84
=
2
×
2
×
3
×
7
LCM =
2
×
2
×
3
×
7
=
84
b.
25
=
5
×
5
15
=
5
×
3
36
=
2
×
2
×
3
×
3
LCM =
2
×
2
×
3
×
3
×
5
×
5
=
900
c.
24
=
2
×
2
×
2
×
3
36
=
2
×
2
×
3
×
3
40
=
2
×
2
×
2
×
5
LCM =
2
×
2
×
2
×
3
×
3
×
5
=
360
d.
27
=
3
×
3
×
3
36
=
2
×
2
×
3
×
3
LCM =
2
×
2
×
3
×
3
×
3
=
108
e. 72
f. 420
Practice HCF and LCM problems
Answer:
sedimentation tank I think so