Question

In a restaurant, the probability that a customer orders steak is 4/10.  The probability of the same customer ordering dessert after their meal is ¼.  What is the probability that a random restaurant customer will order dessert given that they ordered steak?

Answer 1

The probability of two mutually independent events happening one after the other is given by the product of both probabilities. In other words, if there is an x/100 chance of A happening and a y/100 chance of B happening, then the chance of both A and B happening is (x/100)(y/100). 
There is a 4/10 chance that a random customer will order steak. Of that 4/10, there is a 1/4 chance that they will order dessert. So, the probability that both will happen is (4/10)(1/4) = 1/10.