Thread: Simple stats problem : Unable to get final answer

I have a simple stats problem where the following table is given.

Speed (Km/h)--------Frequency-----------Cumulative Frequency

0<s<=40--------------14----------------------14
40<s<=60-------------51----------------------65
60<s<=70-------------157---------------------222
70<s<=80-------------141---------------------363
80<s<=100------------37----------------------400

I am asked to find the median which i can find easily 51, but the standard deviation i tried all sorts of values but unable to get the given answer which is 64.6. I am getting like 13.67. Can someone guide me out on this issue ?

Originally Posted by tester85

I have a simple stats problem where the following table is given.

Speed (Km/h)--------Frequency-----------Cumulative Frequency

0<s<=40--------------14----------------------14
40<s<=60-------------51----------------------65
60<s<=70-------------157---------------------222
70<s<=80-------------141---------------------363
80<s<=100------------37----------------------400

I am asked to find the median which i can find easily 51, but the standard deviation i tried all sorts of values but unable to get the given answer which is 64.6. I am getting like 13.67. Can someone guide me out on this issue ?

The standard deviation cannot be 64.6.

The mean is:



where is the cell mark and is the frequency of the th cell respectivly.

then:



is the variance and is the standard deviation.


CB

I use a one of the standard deviation formula.

xifi = 26940 fi = 1943530

= 1/400[ 1943530 - /400 ] = 13.67

According to the formula stated i got 67.35 for the mean is that correct ?

May i know what is the value you got for the mean and standard deviation?