What is the value of x if \(\rm {1\over 9!}+{1\over 8!}={x\over 10!}\)

  1. 21
  2. 54
  3. 3
  4. 100

Answer (Detailed Solution Below)

Option 4 : 100
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Detailed Solution

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Concept:

Some useful formulas are:

n! = n.(n - 1).(n - 2)...3.2.1

Calculation:

Given expression is \(\rm {1\over 9!}+{1\over 8!}={x\over 10!}\)

∴ \(\rm {1\over 9\;\times\; 8!}+{1\over 8!}={x\over 10\;\times \;9\;\times\; 8!}\)

∴ \(\rm {1\over 8!}({{1\over 9} +1})={x\over 10\;\times\; 9\;\times \;8!}\)

∴ \({10\over 9} ={ x\over 10\;\times\; 9}\)

∴ x = 100

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