Two numbers are respectively 20% and 50% of a third number. What per cent is the first number of second?

10%

20%

30%

40%

50%

Let third number is x. Then first no.20%ofx=20x100 Second number=50%ofx=50x100 Percent of first no of second no,=20x10050x100×100=2×10020= 40%