The sum and product of two numbers are 11 and 18 respectively. Then the sum of…
2016
The sum and product of two numbers are 11 and 18 respectively. Then the sum of their reciprocals is:
- A.
2/11
- B.
11/2
- C.
18/11
- D.
11/18
Attempted by 3 students.
Show answer & explanation
Correct answer: D
Concept
For two non-zero numbers x and y, reciprocal fractions are added by using the common denominator xy. Therefore 1/x + 1/y = (x+y)/(xy): the numerator is the original sum and the denominator is the original product.
Application
Let the numbers be x and y. The given conditions are x + y = 11 and xy = 18.
Write the requested sum: 1/x + 1/y.
Use the common denominator xy: 1/x + 1/y = (y+x)/(xy) = (x+y)/(xy).
Substitute the given sum and product: (x+y)/(xy) = 11/18.
Cross-check
The numbers can be 2 and 9 because 2 + 9 = 11 and 2 × 9 = 18. Their reciprocals give 1/2 + 1/9 = (9+2)/18 = 11/18, confirming the calculation independently.
Result
Hence, the sum of the reciprocals is 11/18.
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