= menu. Select binompdf( and press e.
3. You will be returned to the stat editor. Finish off the command by typing
45,0.07) and then press e.
4. Your calculator will fill up L
2
with the probabilities for 0 ≤ x ≤ n successes.
5. We kept L
1
empty because it is useful to indicate the x value that
corresponds to each probability value stored in L
2
. You could go through and
type in each x value manually, but it is often easier to generate these values
automatically. Highlight L
1
and press `S to bring up the 9 menu.
6. Use the right arrow key to scroll to the OPS menu. Select 5:seq( and press
e.
7. You will be brought back to the stat editor. Complete the command by
typing X,X,0,45) and press e. (Note: Press a = to type an
“X.”) The general syntax for this command is seq(X,X,0,n).
8. Your calculator will fill L
1
with the whole numbers from 0 to 45.
9. Together, L
1
and L
2
comprise the binomial probability distribution for n = 45
and p = 0.07. Use the ; and : keys to scroll through all the entries in L
1
and L
2
.
Working with a binomial probability distribution
1. Let’s use the distribution we just generated to find the probability that at least one of the 45
donors has type O-negative blood. The tedious approach would be to add up P(x = 1) + P(x = 2) + P(x
= 3) +. . .+ P(x = 45). Don’t! Instead, take advantage of the fact that the complement of “at least
one” is “none.” Thus, P(1 ≤ x ≤ 45) = 1 - P(x = 0) = 1 - 0.0381709250 = 0.962. Remember to hold off
rounding to 3 significant figures until the end.
2. Next, let’s find the probability that no more than three of the donors have type O-negative blood.
To do so, we need to find P(x = 0) + P(x = 1) + P(x = 2) + P(x = 3). You could write down the
corresponding probabilities from L
2
and then add them up.
3. Alternatively, we can use the sum command and specify the range of items in
L
2
that we wish to add up. The key is to remember that the first item in
the list, L
2
(1), corresponds to P(x = 0); that is, the row number corresponds
to x + 1. Press `S for the 9 menu and scroll right for the MATH
menu. Scroll down to 5:sum( and press e.
4. The syntax for the sum command is sum(list,start,end). For this
example, type `2,1,4) and press e. This command tells
your calculator to sum the contents of rows 1 through 4 in L
2
. We find that
P(x ≤ 3) = 0.613. In other words, there is a 61.3% chance that no more than
three of the 45 donors have type O-negative blood.
Copyright © 2007 by Laura Schultz. All rights reserved. Page 2 of 3