If 30% of a = b then b% of 50 is the same as:

15% of a

30% = \(\frac{3}{10}\)

30% of a = b

 \(\frac{3}{10}\) × a = b

3a = 10b

\(\frac{a}{b }\) = \(\frac{10}{3}\)

Now b% of 50 = 3% of 50

= \(\frac{3}{100}\) ×50 = 1.5

Now , By using option one by one . we find that only option 3 has same value as  b% of 50

i.e 15% of a = \(\frac{15}{100}\) × 10 = 1.5

Hence , 15% of a  is correct answer .