Answer:
The number of double dip sundae that can be created with 1 topping is:
  825
Explanation:
Since, there are 10 different flavors and same flavor can be used for both the dips.
Also, there are a total of 15 different toppings.
Hence, the number of different double dip sundae that can be created with 1 topping is:
 825
( Since, the order in which the two sundae are placed does not matter. Hence, we need to use the method of combination.

As 
 denotes the number of ways of choosing of 2 different toppings from the 10 flavors and the addition 10 term represent the 10 cases case in which both the dips are of same flavor
 denotes the number of ways of choosing of 2 different toppings from the 10 flavors and the addition 10 term represent the 10 cases case in which both the dips are of same flavor
Hence,
 )
)