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can help me on this question please..... a level maths Watch

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    The speeds of a vechile passing a checkpoint were measured over a period of one hour,to the nearest mph.The date is collected is shown int he grouped frequency table.

    speed mph no of vechiles
    21 - 30 4
    31-40 7
    41-50 38
    51-60 42
    61-65 5
    66-70 3
    71-75 1

    a. write down the modal class
    b. calculate the difference,to two decimal places,between the median and the mean estimated speeds
    c. The speed limit on the road is 60mph.Work out an estimate for the percentage of cars that exceeded the speed limit.

    The modal class is the class with the highest frequency. Find the median by calculating the position it should be in (n + 1)/2 and then use the amount into the group it is to work out which number that is. The mean is taking the midpoint of each class, multiplying it by the frequency then dividing by the total frequency. The percentage that exceed the speed limit is finding the percentage of cars which are in a class which has a speed of above 60 mph. Hopefully you can answer it from this!
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