Measures of central tendency

The frequency distribution of the verbal scores on the SAT test for students at a high school is shown below

scores number of students

200-250 9

250-300 14

300-350 23

350-400 30

400-450 33

450-500 28

500-550 18

550-600 12

600-650 7

650-700 3

700-750 1

750-800 1

What is the mean of the verbal scores at the high school

I know there are 179 student I added them up

Then I guess I have to find the sum of all the scores which I got to be 70175

What I did for example was 200+250 divided by times nine to get 2025

then I did 70175/179 But I get the wrong answer.(Angry)

Re: Measures of central tendency

Pick the number half way in each class interval

$\displaystyle \displaystyle \bar{x} = \frac{225\times 9 +275\times 14 +\dots + 775\times 1}{179}$