If the difference and product of two numbers are 5 and 36, respectively, what…

2019

If the difference and product of two numbers are 5 and 36, respectively, what is the difference between their reciprocals?

  1. A.

    5/36

  2. B.

    5/9

  3. C.

    31/36

  4. D.

    9/5

Attempted by 3 students.

Show answer & explanation

Correct answer: A

Concept

For two nonzero numbers x and y, subtracting their reciprocals requires a common denominator: 1/y - 1/x = (x - y)/(xy).

Thus, when the difference x - y and the product xy are known, the reciprocal difference can be obtained directly from their ratio.

Application

  1. Let the two numbers be x and y, with x - y = 5 and xy = 36.

  2. Write the reciprocal difference as 1/y - 1/x = (x - y)/(xy).

  3. Substitute the given values: (x - y)/(xy) = 5/36.

  4. Therefore, the difference between the reciprocals is 5/36.

Cross-check

A factor pair satisfying the conditions is x = 9 and y = 4. Then 1/4 - 1/9 = (9 - 4)/36 = 5/36, confirming the result.

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