Since there are three types of coupons (skiing, snow tubing, and sleigh rides) and each participant has an equal chance of receiving any one of them, the probability of receiving a coupon for sleigh rides is \( \frac{1}{3} \).
To find the expected number of participants who would receive a coupon for sleigh rides, you multiply the total number of participants by the probability of receiving that coupon:
\[ \text{Expected number of sleigh ride coupons} = 900 \times \frac{1}{3} = 300 \]
Thus, the expected number of people who would receive a coupon for sleigh rides is 300.