3. ?Suppose the waiting time to get food after placing an order at a fast-food restaurant is ?exponentially distributed with a mean of 60 seconds. If a randomly selected customer ?orders food at the...

3. ?Suppose the waiting time to get food after placing an order at a fast-food restaurant is ?exponentially distributed with a mean of 60 seconds. If a randomly selected customer ?orders food at the restaurant, what is the probability that the customer will have to wait ?at least two minutes? 4. ?A family has two children – one male child and the other a female child. Both the ?children are grown up and their daily expenditure is believed to be normally distributed ?with a mean of Rs.80 and Rs.60 for the male and the female child with standard ?deviation of Rs.20 and Rs.10 respectively. Find the probability that the two child ?together have an expenditure of more than Rs. 160.