If 45% of (X -Y) = 30% of (X + Y), then what percentage of X is Y ?

20%

According to question ,

45% of (X -Y) = 30% of (X - Y)

\(\frac{45}{100}\) × (X - Y) = \(\frac{30}{100}\) × (X + Y) 

\(\frac{9}{20}\) × (X - Y) = \(\frac{3}{10}\) × (X + Y)

9× (X - Y) = 6 × (X + Y)

9X - 9Y = 6X + 6Y

3X = 15Y

X = 5Y

Let Y = 100 & X = 500

So , required percentage = \(\frac{100}{500}\) × 100

= 20%