i have to create a box and whisker plot what is the three quartiles of the followin numbers

There are THREE quartiles. Start with the second quartile, Q_{2}, also known as the median. It divides the data in half. To find it, put the data in order.

12 10 11 7 9 10 5

becomes

5, 7, 9, **10**, 10, 11, 12

The number which falls in the middle of the list is the median. In this case the median is 10. (For data sets with an odd number of entries, the median is always one of the data points. For an even number, you take the average of the two middle-most data points. Here we have an odd number.)

Q2 = medain = 10.

Now, for Q1 and Q3, the other quartiles, do the same thing on the lower and upper halves of the data set. For Q1:

5, 7, 9, **10**

**
**Q1 is the average of the two points in the middle: (7+9)/2 = 8 = Q1.

For Q2:

**10**, 10, 11, 12

Q2 = (10+11)/2 = 10.5

So your THREE quartiles are 8, 10, and 10.5.