
The harmonic mean of two numbers is 4 and the arithmetic and geometric mean satisfy the relation . Find the numbers.
Answer
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Hint: Here, we will proceed by developing an relation between the arithmetic mean and the geometric mean o the two numbers apart from the one given in the problem with the help of the formula i.e., Arithmetic mean Harmonic mean = .
Complete Step-by-Step solution:
Let the numbers be a and b.
Given, harmonic mean of these numbers (i.e., a and b) is H = 4
Also, given that where A represents arithmetic mean of these numbers (i.e., a and b) and G represents geometric mean of these numbers (i.e., a and b)
According to the relation between arithmetic mean, geometric mean and harmonic mean of any two numbers, we have
Arithmetic mean Harmonic mean =
So,
Substituting H = 4 in the above equation, we get
By substituting equation (2) in equation (1), we get
Put in equation (2), we get
As we know that the arithmetic mean of two numbers a and b is given as
By comparing equations (3) and (5), we get
Also we know that the geometric mean of two numbers a and b is given as
By comparing equations (4) and (7), we get
By substituting the value from equation (6) in equation (8), we get
Either or
Put b=3 in equation (6), we get
Put b=6 in equation (6), we get
When b=3, then a=6 and when b=6, then a=3
Therefore, the required two numbers are 6,3.
Hence, option A is correct.
Note: In this particular problem, we have obtained two equations in two variables (which are the numbers a and b) and then we will solve these two equations with the help of substitution method in order to get the values corresponding to these two numbers. Here, the numbers obtained are either 3,6 or 6,3 which are both the same and depend only on the sequence that which number comes first.
Complete Step-by-Step solution:
Let the numbers be a and b.
Given, harmonic mean of these numbers (i.e., a and b) is H = 4
Also, given that
According to the relation between arithmetic mean, geometric mean and harmonic mean of any two numbers, we have
Arithmetic mean
So,
Substituting H = 4 in the above equation, we get
By substituting equation (2) in equation (1), we get
Put
As we know that the arithmetic mean of two numbers a and b is given as
By comparing equations (3) and (5), we get
Also we know that the geometric mean of two numbers a and b is given as
By comparing equations (4) and (7), we get
By substituting the value
Either
Put b=3 in equation (6), we get
Put b=6 in equation (6), we get
When b=3, then a=6 and when b=6, then a=3
Therefore, the required two numbers are 6,3.
Hence, option A is correct.
Note: In this particular problem, we have obtained two equations in two variables (which are the numbers a and b) and then we will solve these two equations with the help of substitution method in order to get the values corresponding to these two numbers. Here, the numbers obtained are either 3,6 or 6,3 which are both the same and depend only on the sequence that which number comes first.
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