Data Question

[test]

Does anyone know how to find the mean and standard deviation of grouped data that does not have a mid interval.


Store 1 20%
Store 2 20%
Store 3 60%

and a total of 200 people shop at these shops. I know how to do it if there is a mid interval but not sure hwo to do this.

[Carz n Compz]

To find mean (average) you must add all the numbers and divide by the # of numbers. In your case shop 1 and 2 have 40 people and shop 3 has 140. The average amount of people at each store is 66.

[AMD]

http://mathworld.wolfram.com/StandardDeviation.html