The total tickets sold at the fair = 50 tickets.
Kayla and Bianca each bought one ticket, it could be any numbered. We can start with anyone and find their probability.
If Kayla got ticket numbered #7, its probability would be 1 out of 50.
Then there would be 49 tickets remaining for Bianca at the fair.
If Bianca got ticket numbered #10, it probability would be 1 out of 49.
Total probability of (Kayla getting #7 AND Bianca getting #10) would be 1/(50x49) = 1/(2,450) = 0.0004081 = 0.0408%.
Hence, final answer is