Since there are three activities (skiing, snow tubing, and sleigh rides) and each has an equal chance of being selected, each activity has a probability of 1/3.
To find the expected number of participants receiving a coupon for sleigh rides, multiply the total number of participants by the probability of receiving that coupon:
\[ \text{Expected number} = \text{Total participants} \times \text{Probability of sleigh rides} \]
\[ \text{Expected number} = 900 \times \frac{1}{3} = 300 \]
Thus, the expected number of people who would receive a coupon for sleigh rides is 300.