In a lottery there are 10 prizes and 25 blanks.

Total number of lottery tickets = 10 + 25 = 35
Number of prizes = 10

Let  E be the event of getting a prize.

$\therefore \mathrm{P}($ getting a prize $)=\mathrm{P}(\mathrm{E})=\frac{\text { Number of outcomes favourable to } \mathrm{E}}{\text { Number of all possible outcomes }}$

$=\frac{10}{35}=\frac{2}{7}$

Thus, the probability of getting a prize is $\frac{2}{7}$.