The Grade 7 class at Gauss Public School has sold 120 tickets for a lottery. One winning ticket will be drawn. If the probability of one of Mary's tickets being drawn is $\frac{1}{15}$, how many tickets did she buy?
(A) 5
(B) 6
(C) 7
(D) 8
(E) 9
The probability that Mary wins the lottery is equal to the number of tickets that Mary bought divided by the total number of tickets in the lottery.

We are told that the probability that Mary wins is $\frac{1}{15}$.

Since there were 120 tickets in total sold, we would like to write $\frac{1}{15}$ as a fraction with 120 in the denominator.

Since $120 \div 15=8$, then we need to multiply the numerator and denominator of $\frac{1}{15}$ each by 8 to obtain a denominator of 120 .

Therefore, the probability that Mary wins is $\frac{1 \times 8}{15 \times 8}=\frac{8}{120}$. Since there were 120 tickets sold, then Mary must have bought 8 tickets.

ANSWER: (D)