If there are three winter activities (skiing, snow tubing, and sleigh rides) and each participant has an equal chance of receiving a coupon for any one of them, the probability of receiving a coupon for sleigh rides is \( \frac{1}{3} \).
To find the expected number of participants receiving a coupon for sleigh rides, you can calculate it as follows:
\[ \text{Expected number of sleigh ride coupons} = \text{Total participants} \times \text{Probability of sleigh ride coupon} \]
\[ \text{Expected number of sleigh ride coupons} = 900 \times \frac{1}{3} = 300 \]
Therefore, the expected number of people who would receive a coupon for sleigh rides is 300.