Four books, one each on physics, chemistry, mathematics, and biology are about to be stacked on a shelf. if the books are stacked randomly, what is the probability the mathematics book is on top?

 The required probability is 25%.

Step-by-step explanation:  Given that four books, one each on physics, chemistry, mathematics, and biology are about to be stacked on a shelf.

We are to find the probability that the mathematics book is on top if the books are stacked randomly.

Let, 'M' be the event that the topmost book is of mathematics.

Then, n(M)=1.

Let 'S' represents the sample space for the experiment.

Then, n(S) = 4.

Therefore, the probability  that the mathematics book is on top is given by

Thus, the required probability is 25%.

ab will be equal to