Question

find the mean and model class
Class boundaries Frequency
0.5–3.5 11
3.5–6.5 12
6.5–9.5 4
9.5–12.5 2
12.5–15.5 1

Answer 1

can anyone tell me the equation of how to find the answer? please

Answer 2

You should find first a point that represents the interval. So to each interval exists one point, the mid point, whose form is,
\[x_i=(a+b)/2\]
Once you get the midpoint for each interval, you can find the mean, with the formula,
\[\overline{x}=\frac{x_1\cdot f_1+x_2\cdot f_2+x_3\cdot f_3+\ldots+x_n\cdot f_n}{n}\]

Answer 3

Also the modal class is the interval with highest frequency. In this case, [3.5,6.5].

Answer 4

I am a little confused. how do I find the class boundary

Answer 5

the class boundary is already given to me but I have to figure the mean the full question is
class boundary frequency
0.5-3.5 11
3.5-6.5 12
6.5-9.5 4
9.5-12.5 2
12.5-15.5 1
I have to find the mean and the modal.

Answer 6

Well, you need the class average to find the mean with the formula I wrote.

Answer 7

For example, the class average for the first interval is,
\[(0.5+3.5)/2=2\]

Answer 8

so I will do that all of those class boundaries and then divide by 5?

Answer 9

You find all the class average, and you'll obtain a new table.

Answer 10

You don't need to divide by 5 the class average.

Answer 11

i don't understand. I thought to find the mean you

Answer 12

class average frequency
2 11
5 12
8 4
11 2
14 1

Answer 13

i had to all of the values and then divide

Answer 14

add

Answer 15

oh

Answer 16

Now, multiply each class average by its frequency, add, and divide by the sum of all frequencies.
\[Mean=\frac{2\cdot 11+5\cdot 12+8\cdot 4+11\cdot 2+14\cdot 1}{30}\]

Answer 17

ok so where did you come up with 30?

Answer 18

It is the sum of all frequencies.

Answer 19

I am totally confused now. This is my first class of statistics and I am completely lost.

Answer 20

Take a tour on this webpage, may be it helps you
http://www.mathsteacher.com.au/year8/ch17_stat/03_freq/freq.htm#M1

Answer 21

And this, for the mean,
http://ncalculators.com/math-worksheets/how-to-calculate-class-interval-arithmetic-mean.htm

Answer 22

ok thanks i will do that.

Answer 23

I appreciate your help

Answer 24

You're welcome. ;)

Answer 25

btw my answer is 5 right?