Problems based on Numbers Test 4

Question : 15 of 40

Marks: +1, -0

A positive number when decreased by 4, is equal to 21 times the reciprocal of the number. Find the number.

Solution:

Let the positive number be x, then

(x - 4) = 21 ×1/x

⇒ x^2 - 4x - 21 = 0

⇒ x^2 - 7x + 3x - 21 = 0

⇒ x(x - 7) + 3(x - 7) = 0

⇒ (x + 3) (x- 7) = 0

Either, x = – 3 (Impossible) or, x = 7
Hence, number = 7

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