1.

The mean of the above data is `5.5` . Find the missing frequency y in the above distribution . (a) 6 `" "` (b) 8 `" "` (c) 15 `" "` (d) 11

Answer» Given AM = 5.5
`sumf*x = 2xx 3 + 4 xx 5 + 6 xx 6 + 8xy`
`= 6 + 20 + 36 + 8y`
`sumf * 2= 62 + 8y " " (1) `
Now `sum f = 3 + 5 + 6 + y`
`sum f = 14 + y " " (2) `
Using Eqs. (1) and (2)
`AM = (sum f*x)/(sum f) implies 5.5 = (62 + 8y)/(14 + y)`
`implies 5.5 (14 + y) = 62 + 8y`
`implies 77 + 5.5 y = 62 + 8y`
`implies 8y - 5.5y = 77 - 62 `
`implies 2.5 y = 15`
`implies y = 6`
`therefore` Hence , option (a) is the correct answer .


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