A number is selected at random from first 50 natural numbers.

Total number of outcomes = 50

Let E be the event of getting a number which is a multiple of 3 and 4.

Now, the common multiples of 3 and 4 among first 50 natural numbers are 12, 24, 36 and 48.

So, the favourable number of outcomes are 4.

$\therefore$ Required probability $=\mathrm{P}(\mathrm{E})=\frac{\text { Favourable number of outcomes }}{\text { Total number of outcomes }}=\frac{4}{50}=\frac{2}{25}$