The Geometric mean of four numbers 2, X, 16, 32 is 8. What is the value of X ?

The geometric mean of four numbers is the fourth root of their product, so $2 \times X \times 16 \times 32 = 8^4 = 4096$. Since $2 \times 16 \times 32 = 1024$, we get $1024X = 4096$ and $X = 4$. Check: the product of 2, 4, 16 and 32 is 4096, whose fourth root is 8. Taking $X = 8$ confuses the geometric mean with one of the numbers.