Heres the question:
The Royal Automobile Association defines peak-time as 6 am to 6 pm, Monday to Friday. It records the number of vehicle breakdowns reported per hour. The figures for a random sample of 40 peak-time hours in a certain area are as follows.
i. Find the mean and variance of the data.
I worked out the mean to be 0.5, which is right, but im stuck on the variance part.
I know the formula for variance to be
So i need to find , which is
Im a bit stuck on the part due to one of the x values being '4 or more'. Normally i wouldn't have a problem with these sorts of questions, but they usually just have single values for x.
How would i use '4 or more' in the formula. Should i just do ... etc, or is there something else i need to do?
Thanks in advanced.