Answer:
Probability = 72.2%
Explanation:
A number line contains points Q, R, S, and T with coordinated 24, 28, 29, and 42 respectively.
Now if a point lies on QT then the length of QT= coordinate of T - coordinate of Q 
= 42 - 24 
= 18
If a point lies on ST then the length of ST = coordinate of T - coordinate of S
= 42 - 29
= 13
Now we know Probability of an event = 

Probability = 

 = 72.2%
Therefore, probability that a point chosen on QT will lie on ST will be 72.2%