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:

  1. A.

    2/11

  2. B.

    11/2

  3. C.

    18/11

  4. 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

  1. Let the numbers be x and y. The given conditions are x + y = 11 and xy = 18.

  2. Write the requested sum: 1/x + 1/y.

  3. Use the common denominator xy: 1/x + 1/y = (y+x)/(xy) = (x+y)/(xy).

  4. 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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