1. Determine the middle term in the binomial expansion of (x + y)20.
2. Determine the middle term in the binomial expansion of (x + y)10.
3. Determine the coefficient of x2 in the expansion of (1 + x)4.
4. Determine the coefficient of x3 in the expansion of (2 + x)6.
5. Determine the coefficient of x4y7 in the binomial expansion of (x + y)11.
6. Determine the coefficient of x9y4 in the binomial expansion of (x + y)13.