Aptitude - Problems on H.C.F and L.C.M - Discussion
Discussion Forum : Problems on H.C.F and L.C.M - General Questions (Q.No. 30)
30.
If the sum of two numbers is 55 and the H.C.F. and L.C.M. of these numbers are 5 and 120 respectively, then the sum of the reciprocals of the numbers is equal to:
Answer: Option
Explanation:
Let the numbers be a and b.
Then, a + b = 55 and ab = 5 x 120 = 600.
 The required sum = |
1 | + | 1 | = | a + b | = | 55 | = | 11 |
| a | b | ab | 600 | 120 |
Discussion:
37 comments Page 4 of 4.
Abhi said:
8 years ago
The product of two no=2448 and the difference of the two no is equal to their HCF and the HCF is a perfect square. Find the no?
Bhuttoo said:
7 years ago
Please, anyone help me to solve this question for me.
Two bulbs flash at regular intervals of 30 and 36 seconds respectively. They flash together at 10.45. At what time will they flash together?
(a) a second time.
(b) a 5th time.
Two bulbs flash at regular intervals of 30 and 36 seconds respectively. They flash together at 10.45. At what time will they flash together?
(a) a second time.
(b) a 5th time.
Milan said:
7 years ago
@Bhuttoo & @Lucas.
1st of all you should find the lcm that is 180 second or 3 minutes. It means they flash together at every 3miunites.
They will flash together.
(a) at 10:48 for the second time.
(b) at 11:00 for 5th time.
1st of all you should find the lcm that is 180 second or 3 minutes. It means they flash together at every 3miunites.
They will flash together.
(a) at 10:48 for the second time.
(b) at 11:00 for 5th time.
Aakash Choudhary said:
5 years ago
Let the number be 5a and 5b.
Given HCF= 5 LCM =120.
Sum=55.
5a+5b=55.
=> a+b=11 ------> (1)
By property product of numbers= LCM*HCF.
5a*5b= 5*120
=> 5ab= 120 --------> (2).
Now sum of reciprocal of numbers:-
(1/5a) + (1/5b) = a+b/5ab.
Putting values from (1) and (2).
(1/5a) + (1/5b)= 11/120.
Given HCF= 5 LCM =120.
Sum=55.
5a+5b=55.
=> a+b=11 ------> (1)
By property product of numbers= LCM*HCF.
5a*5b= 5*120
=> 5ab= 120 --------> (2).
Now sum of reciprocal of numbers:-
(1/5a) + (1/5b) = a+b/5ab.
Putting values from (1) and (2).
(1/5a) + (1/5b)= 11/120.
(2)
Balamurugan said:
4 years ago
1/a+1/b=a+b/ab. How is come??
Maha said:
4 years ago
@Balamurugan.
By Cross multiply, you well get this.
By Cross multiply, you well get this.
ANSHUL JYOTI said:
2 years ago
@Nirmala.
7/16 + 5/24 = LCM ( 16, 24) = 48.
Therefore (7x3)/(16x3) + (5x2)/(24x2) = 31/48.
7/16 + 5/24 = LCM ( 16, 24) = 48.
Therefore (7x3)/(16x3) + (5x2)/(24x2) = 31/48.
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