Hi
Using TI or similarly an inexpensive calculator like a Casio fx-115 ES plus
probability that at least two of them choose the exact same pizza
n = 3 ,  p = 1/4 (4 choices of toppings)
P(x ≥ 2) = 1  -  P(x ≤ 1) = 1 - binomcdf(3,1/4, 1) = 1 -  .84375 = .1563
0r
Using  
 
 
P(x ≥ 2) = 1 - .42187 - .42187 = .1563
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probability that at least two of them choose the exact same dessert
n = 3 ,  p = 1/3 (3 choices of desserts)
P(x ≥ 2) = 1  -  P(x ≤ 1) = 1 - binomcdf(3,1/3, 1)

probability that at least two of them choose the exact same topping and dessert
n = 3 ,  p = 1/12 ( 4*3 = 12 choices for both)
P(x ≥ 2) = 1  -  P(x ≤ 1) = 1 - binomcdf(3,1/12, 1)
Wish You the Best in your Studies.