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A positive number when decreased by 4 becomes 21 times its reciprocal. The number is (a) 8 (b) 7 (c) 6 (d) 5 |
Answer» (b) 7 \(x\) - 4 = 21 x \(\frac1x\) ⇒ x2 - 4x = 21 ⇒x2 - 4x - 21 = 0 ⇒ (x - 7)(x + 3) = 0 ⇒ x = 7, - 3 ⇒ x = 7. |
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