A number is doubled. By what % must it be reduced to get back the original number.
Explanation:
Let the initial number be 100. After doubling, the number becomes 200.
Now, 200 should reduce to 100.
∴ % change = (200 - 100)/200 × 100% = 50%
Alternately, If the number is multiplied with 2 (doubled), it should be multiplied with 1/2 (reciprocal) to get back the original number.
∴ multiplication factor when reducing = 1/2
⇒ % change = (mf - 1) × 100% = (1/2 - 1) × 100% = - 50% [- indicated % decrease.]
Hence, option (c).
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