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    For linear interpolation , when are you meant to use the upper and lower bounds of the classes and when are you meant to just use the normal base. I get really confused with this.
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    could you post an example question ?
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    (Original post by the bear)
    could you post an example question ?
    http://i.imgur.com/7gtS9ZL.png

    Like this one here, im not sure whether i am supposed to use the upper and lower bounds or just use the base values for the classes (the column with time in seconds)
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    (Original post by Atiq629)
    http://i.imgur.com/7gtS9ZL.png

    Like this one here, im not sure whether i am supposed to use the upper and lower bounds or just use the base values for the classes (the column with time in seconds)
    since there are 85 items, you look for the ( 85 + 1 ) /2 th item... which is number 43.

    you count up the frequencies to see which group number 43 is in.

    it is in the 70 - 80 group. the three previous groups contain 29 items so we need another 14 from the fourth group which contains 25 altogether....

    so we say that we need to go 14/25 of the way into the fourth group....

    can you continue ?
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    (Original post by the bear)
    since there are 85 items, you look for the ( 85 + 1 ) /2 th item... which is number 43.

    you count up the frequencies to see which group number 43 is in.

    it is in the 70 - 80 group. the three previous groups contain 29 items so we need another 14 from the fourth group which contains 25 altogether....

    so we say that we need to go 14/25 of the way into the fourth group....

    can you continue ?
    Not sure what you mean by the last part but i use the formula method. B+q/2 - cf / f *cw .

    B is your base value and in some mark schemes it doesnt use the whole number of the base value but upper and lower bounds which i dont understand...
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    since the width of the fourth class is 10 units, you need to move 14/25 of the way along 10 units... this gives a distance of 5.6 which needs to be added to the left hand end of the group.
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    For the interpolation do 85/2 which gives 42.5, you don't need to do +1 because it's continuos. Then that gives 42.5, find in what class the 42.5 is which is in the 70-80 class. Then you'll notice up to that class there are 29 terms so do 42.5-29 giving 13.5. Now you need to find 13.5/25 of the way through 70-80 and add that to 70. This can be done by 70 +[(13.5)/25]x(80-70) giving you the answer of 75.4
 
 
 
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