Question : A positive number, when decreased by 4, is equal to 21 times the reciprocal of this number. The number is:
Option 1: 3
Option 2: 7
Option 3: 5
Option 4: 9
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Correct Answer: 7
Solution : Let the positive numbers be $x$ and $\frac{1}{x}$. According to the question, $ x-4=\frac{21}{x}$ $x^{2}-4x-21 =0$ $x^{2}-7x+3x-21 =0$ $x(x-7)+3(x-7)=0$ $(x-7)(x+3) =0$ $x-7=0$ or $x+3=0$ $\therefore x=7$ or $x=-3$ $x$ cannot be –3, as it is a positive number. Hence, the correct answer is 7.
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Question : Directions: If 4 × 9 × 3 = 4 and 5 × 3 × 1 = 3, then 9 × 9 × 7 = ?
Question : Directions: By Interchanging the given two numbers which of the following equations will be not correct? 7 and 9
Question : Directions: By Interchanging the given two numbers which of the following equations will be correct? 7 and 4
Question : What is the value of S $=\frac{1}{1×3×5}+\frac{1}{1×4}+\frac{1}{3×5×7}+\frac{1}{4×7}+\frac{1}{5×7×9}+\frac{1}{7×10}+....$ Up to 20 terms, then what is the value of S?
Question : Directions: By Interchanging the given two numbers which of the following equations will be correct? 5 and 9
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