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Explanation
- A positive number when decreased by 4.
- Is equal to 21 times the reciprocal of the number.
- The number will be figure out in this way.
Let suppose the positive number is y.
21 times the reciprocal of the number
21 x 1/y
Positive number when decreased by 4
y – 4 = 21 x 1/y ________ (i)
Through equation (i) we can easily find out the value of y (y = 7).
To Find
Number = ?
Solution
Let suppose
Number = y
According to the given condition
y – 4 = 21 x 1/y
y(y – 4) = 21
y2 – 4y = 21
y2 – 4y – 21 = 0
y2 – 7y + 3y – 21 = 0
y(y – 7) + 3(y – 7) = 0
(y – 7)(y + 3) = 0
y + 3 = 0 & y – 7 = 0
y = -3 (not possible) & y = 7 (possible)
Required Number = 7 answer
Conclusion
So, the required number is 7 which when decreased by 4 is equal to 21 times the reciprocal of the number.