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Home ‣ Aptitude ‣ Problems on H.C.F and L.C.M Comments
- Question
- Six bells commence tolling together and toll intervals of 2, 4, 6, 8, 10 and 12 seconds respectively. In 30 minutes, how many times do they toll together?
Options- A. 4
- B. 10
- C. 15
- D. 16
- Correct Answer
- 16
ExplanationL . C . M of 2, 4, 6, 8, 10 and 12 is 120
So the bells will toll together after 120 second i,e 2 minutes. In 30 min. they will together in (30/2) + 1 times, i.e 16 times. - 1. Three pieces of timber 42 m, 49 m and 63 m long have to be divided into planks of the same length, What is the greatest possible length of each plank?
Options- A. 7 m
- B. 14 m
- C. 42 m
- D. 63 m Discuss
- 2. Three different containers contain different qualities of mixtures of milk and water, whose measurement are 403 kg, 434 kg and 465 kg. What biggest measure must be there to measure all the different qualities exactly?
Options- A. 1 kg
- B. 7 kg
- C. 31 kg
- D. 41 kg Discuss
- 3. Five bells begin to toll together and toll respectively at intervals of 6, 7, 8, 9 and 12 seconds. How many times they will toll together in one hour , excluding the one at the start?
Options- A. 3
- B. 5
- C. 7
- D. 9 Discuss
- 4. 21 mangoes trees, 42 apples trees and 56 oranges trees have to be planted in rows such that each row contains the same number of trees one variety only. Minimum number of rows in which the above trees may be planted is?
Options- A. 15
- B. 17
- C. 3
- D. 20 Discuss
- 5. The Sum of two number is 1215 and their H.C.F is 81, how many pairs of such number can be formed? Find them?
Options- A. 1
- B. 2
- C. 3
- D. 4 Discuss
- 6. The least multiple of 7, which leaves a remainder of 4, when divided by 6, 9, 15 and 18 is?
Options- A. 74
- B. 94
- C. 184
- D. 364 Discuss
- 7. The largest natural number, which exactly divides the products of any four consecutive natural numbers, is?
Options- A. 6
- B. 12
- C. 24
- D. 120 Discuss
- 8. The total number of prime factors of the products (8) 20, (15) 24, (7) 15 is?
Options- A. 59
- B. 98
- C. 123
- D. 138 Discuss
- 9. The traffic lights at three different road crossings changes after every 48 sec., 72 sec. and 108 sec. respectively. If they all change simultaneously at 8 : 20 : 00 hrs, then they will again change simultaneously at?
Options- A. 8 : 27 : 12 hrs.
- B. 8 : 27 : 24 hrs.
- C. 8 : 27 : 36 hrs.
- D. 8 : 27 : 48 hrs. Discuss
- 10. Four metal rods of lengths 78 cm, 104 cm, 117 cm and 169 cm are to be cut into parts of equal length. Each part must be as long as possible. What is the maximum number of pieces that can be cut?
Options- A. 27
- B. 36
- C. 43
- D. 480 Discuss
Problems on H.C.F and L.C.M
Search Results
Correct Answer: 7 m
Explanation:
Greatest possible length of each plank = H.C.F of 42, 49, 63 = 7 m
Correct Answer: 1 kg
Explanation:
Biggest measure = H.C.F. of 403, 434 and 465
= 31 kg
Correct Answer: 7
Explanation:
L.C.M of 6, 7, 8, 9, 12 is 504
So, the bells will toll together after 504 sec.
In hour, they will toll together
= (60 x 60) / 504 times
= 7 times
Correct Answer: 17
Explanation:
H.C.F. of 21, 42, 56 = 7
Number of rows of mango trees, apple trees and oranges trees are 21/7 = 3, 42/7 = 6 and 56/7 = 8
? Required number of rows = (3 + 6 + 8 ) = 17
Correct Answer: 4
Explanation:
Let the number be 81a and 81b where a and b are two numbers prime to each other.
? 81a + 81b = 1215
? a + b = 1215/81 = 15
Now, find two numbers, whose sum is 15, the possible pairs are (14, 1) , (13, 2), (12, 3), (11, 4), (10, 5), (9, 6 ), (8, 7) of these the only pairs of numbers that are prime to each other are (14, 1) , (13, 2), (11, 4), and (8, 7).
Hence, the required number are
(14 x 81, 1 x 81), (13 x 81, 2 x 81), (11 x 81, 4 x 81), (8 x 81, 7 x 81)
or (1134, 81), (1053, 162), (891, 324), (648, 567)
So, there are four such pairs .
Correct Answer: 364
Explanation:
Let the least multiple of 7 be x, which when divided by 90 leaves the remainder 4. Then, x is of the form 90k + 4
Now, the minimum value of k for which 90k + 4 divisible by 7 is 4
? x = 90 x 4 + 4
= 364
Correct Answer: 24
Explanation:
In any 4 consecutive natural numbers:
Two numbers will be divisible by 2, one of which will be divisible by 4, at least one number will be divisible by 3.
These facts give us a lower bound of 2 x 4 x 3 = 24 for the solution.
But 24 is also the product of the first 4 consecutive natural numbers, so it is also an upper bound.
Correct Answer: 123
Explanation:
Since 2, 3, 5, 17 are prime numbers and
The given expression = (23)20 x (3 x 5)24 x (17)15
= 260 x 324 x 524 x 1715
So the total number of prime factors in the given expression is (60 + 24 + 24 + 15 ) = 123.
Correct Answer: 8 : 27 : 12 hrs.
Explanation:
Interval of changes = (L . C . M of 48, 72, 108) sec. = 432 sec.
So, the lights will simultaneously changes after every 432 seconds i,e 7 min. 12 sec.
So, the next simultaneously changes will take place at 8 : 27 : 12 hrs.
Correct Answer: 36
Explanation:
Given, length of four metal roads are 78, 104, 117 and 169 cm.
Now,
78 = 13 x 2 x 3,
104 = 13 x 2 x 2 x 2,
117 = 13 x 3 x 3,
169 = 13 x 13
Length of each piece of rod as long as possible, HCF = 13 CM
? Number of piece = 6 + 8 + 9 + 13 = 36
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