A number is first decreased by 20%. The decreased number is then increased by 20%. The resulting number is less than the original number by 20. Then the original number is
Options:
A . 400
B . 600
C . 500
D . 200
Answer: Option C Answer: (c) Effective percentage = $(-20 + 20 - {20 × 20}/100)$= - 4% If the number be x, then 4% of x = 20 $x × 4/100 = 20$ $x = {20 × 100}/4 = 500$ Using Rule 3, If an amount is increased by a% and then it is reduced by a% again, then percentage change will be a decrease of $a^2/100%$
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