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Q.

The sum of a number and its reciprocal is 2120. The number is


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a

45

b

 34

c

56

d

65  

answer is A.

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Detailed Solution

Given that the sum of a number and its reciprocal is 2120.
A quadratic equation in the variable x is of the form ax2+bx+c=0, a0 where a, b and c are real numbers
And the sum of the roots is given by ba.
Let’s consider root of the equation is m and according to the given condition its reciprocal is 1m.
Sum of the roots,
m+1m=2120                m2+1m=4120                           20(m2+1)=41
 20m2+20=41m                 20m2-41m+20=0 Now, we will find the roots of the equation 20m2-41m+20=0 and then we will get the value of m.
20m2-41m+20=0
20m2-25m-16m+20=0
5m4m-5-44m-5=0
5m-44m-5=0
5m-4=0 or 4m-5=0
5m=4 or 4m=5
 m=45or m=54 The required number is 45.
Hence, the correct option is 1.
 
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The sum of a number and its reciprocal is 2120. The number is