What is the speed of the train ?
I. The train crosses a signal pole in 14 secs
II. The train crosses another train in 16 secs
III. The train crosses a 200 metres long platform in 24 secs

Let the length of the train be L and let the speed of the train be S. We need to calculate the value of S.

Using Statement 1, 14S = L

Using Statement 2, let the length of another train be T. So, 16S = L+T

Using Statement 3, 24S = L+200

Statement 2 intriduces a new variable T which is the length of another train. As no other information is known about the other train, the equation can't be solved.
However, using Statements 1 and 3, we can find that 10S=200 or S = 20m/s

So, the question can be solved using Statements 1 and 3.