1.

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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