Find x if \(\frac{1}{{5!}} + \frac{1}{{6!}} = \frac{x}{{7!}}\) ?

  1. 100
  2. 36
  3. 49
  4. 64

Answer (Detailed Solution Below)

Option 3 : 49
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Detailed Solution

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CONCEPT:

n! = n × (n - 1) × ...... × 1

CALCULATION:

Given: \(\frac{1}{{5!}} + \frac{1}{{6!}} = \frac{x}{{7!}}\)

As we know that, n! = n × (n - 1) × ...... × 1

⇒ \(\frac{1}{{5!}} + \frac{1}{{6\; \times \;5!}} = \frac{x}{{7 \;\times \;6 \;\times \;5!}}\)

⇒ \(\frac{1}{{5!}} \times \left( {1 + \frac{1}{{6}}} \right) = \frac{1}{{5!}} \times \frac{x}{{42}}\)

⇒ \(1 + \frac{1}{{6}} = \frac{x}{{42}}\)

⇒ x = 49

Hence, option C is the correct answer.

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