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