A number is first decreased by 20%. The decreased number

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

Effective percentage

=		- 20 + 20 -	20 × 20		= – 4%
			100

If the number be x, then
4% of x = 20

⇒ x ×	4	= 20
	100

⇒ x =	20 × 100	= 500
	4

Aliter : Using Rule 3,
Let the number be x

Decrease % =	20²	= 20
	100

x – 4% of x = x – 20

	4x	= + 20
	100

x = 500