LCM and HCF
Factors and Multiples : All the numbers that divide a number completely, i.e., without leaving any remainder, are called factors of that number. For example, 24 is completely divisible by 1, 2, 3, 4, 6, 8, 12, 24. Each of these numbers is called a factor of 24 and 24 is called a multiple of each of these numbers … More on LCM and HCF

HCF

Question 1
Two numbers are in the ratio of 2:9. If their H. C. F. is 19, numbers are:
A
6, 27
B
8, 36
C
38, 171
D
20, 90
Arithmetic Aptitude 4    HCF    Ratio and Proportion    
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Question 1 Explanation: 
Let the numbers be 2X and 9X
Then their H.C.F. is X, so X = 19
∴ Numbers are (2x19 and 9x19) i.e. 38 and 171
Question 2
HCF of two numbers is 11 and their LCM is 385. If the numbers do not differ by more than 50, what is the sum of the two numbers ?
A
132
B
35
C
12
D
36
Numbers    LCM    HCF    
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Question 2 Explanation: 
Product of numbers = LCM x HCF = 11 x 385 = 4235 Let the numbers be of the form 11m and 11n, such that 'm' and 'n' are co-primes. => 11m x 11n = 4235 => m x n = 35 => (m,n) can be either of (1, 35), (35, 1), (5, 7), (7, 5). => The numbers can be (11, 385), (385, 11), (55, 77), (77, 55). But it is given that the numbers cannot differ by more than 50. Hence, the numbers are 55 and 77. Therefore, sum of the two numbers = 55 + 77 = 132
Question 3
Two numbers are in the ratio of 5:7. If their LCM is 105, what is the difference between their squares ?
A
216
B
210
C
72
D
840
Numbers    LCM    HCF    
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Question 3 Explanation: 
Let 'h' be the HCF of the two numbers. => The numbers are 5h and 7h. We know that Product of Numbers = LCM x HCF => 5h x 7h = 105 x h => h = 3 So, the numbers are 15 and 21. Therefore, difference of their squares = 212 - 152 = 441 - 225 = 216
Question 4
Which is the largest number that divides 17, 23, 35, 59 to leave the same remainder in each case ?
A
2
B
3
C
6
D
12
Numbers    HCF    
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Question 4 Explanation: 
Required Number = HCF (23-17, 35-23, 59-35, 59-17) Required Number = HCF (6, 12, 24, 42) = 6
Question 5
The LCM. of two numbers is 30 and their HCF. is 15. If one of the numbers is 30, then what is the other number?
A
30
B
25
C
15
D
20
LCM    HCF    
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Question 5 Explanation: 
Say another number =x product of two numbers = product of HCF and LCM x.30 = 15*30 x=15
Question 6
Express 252 as a product of primes.
A
2 * 2 * 3 * 3 * 7
B
3* 3 * 3 * 3 * 7
C
2 * 2 * 2* 3 * 7
D
2 * 3 * 3 * 3 * 7
HCF    
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Question 7
Which of the following has the most number of divisors?
A
99
B
101
C
176
D
182
HCF    
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Question 7 Explanation: 
99 = 1 * 3 * 3 * 11 101 = 1 * 101 176 = 1 * 2 * 2 * 2 * 2 * 11 182 = 1 * 2 * 7 * 13 Clearly, 176 has the most number of divisors.
Question 8
A perfect number n is a number which is equal to the sum of its divisors. Which of the following is a perfect number?
A
6
B
9
C
15
D
21
HCF    
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Question 8 Explanation: 
6 is divisible by 1, 2 and 3. And, 6 = 1 + 2 + 3.
Question 9
Express 1095/1168 in its simplest form.
A
13/16
B
15/16
C
17/26
D
25/26
HCF    
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Question 10
Find the highest common factor of the following numbers: 4 * 27 * 3125 8 * 9 * 25 * 7 16 * 81 * 5 * 11 * 49
A
180
B
360
C
540
D
1260
HCF    
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Question 11
Calculate the HCF of 36 and 84.
A
4
B
6
C
12
D
18
HCF    
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Question 11 Explanation: 
36 = 2 * 2 * 3 * 3 84 = 2 * 2 * 3 * 7 2 * 2 * 3 = 12.
Question 12
Calculate the HCF of 1.08, 0.36 and 0.9.
A
0.03
B
0.9
C
0.18
D
0.108
HCF    
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Question 12 Explanation: 
Let's rewrite the numbers as 108/100, 36/100 and 90/100. Now, HCF of 108, 36 and 90 is 18. Therefore, 18/100 = 0.18 is our answer.
Question 13
Three numbers are in the ratio 1:2:3 and their HCF is 12. The numbers are:
A
4, 8, 12
B
5, 10, 15
C
10, 20, 30
D
12, 24, 36
HCF    
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Question 14
The sum if two numbers is 528 and their HCF is 33. The number of pairs of numbers satisfying the above condition is:
A
4
B
6
C
8
D
12
HCF    
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Question 14 Explanation: 
Let the required numbers be 33x and 33y. Then, 33x + 33y = 528 But, 528 = 2 * 2 * 2 * 2 * 3 * 11. So, x + y = 16 Co-primes with the sum 16 are: (1, 15), (3, 13), (5, 11) and (7, 9). Hence, 4.
Question 15
The product of two number is 4107. If the HCF of these numbers is 37, then the greater number is:
A
101
B
107
C
111
D
185
HCF    
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Question 15 Explanation: 
Let the required numbers be 37x and 37y. Then, 37x * 37y = 4107 So, x * y = 4107/(37*37) = 3. Co-primes with product 3 are (1,3). Therefore, the greater number = 3 * 37 = 111.
There are 15 questions to complete.


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