It is reported that in the Congress, 60% are in favor of the Death Penalty
Law. If a group of 10 congressmen is chosen at random, find the probability
that at least 8 are in favor of the Death Penalty Law.
a. 0.16729 b. 0.26729 c. 0.36729 d. 0.46729
Since the TI-84 calculator only calculates the lower values, (fewer than or
equal to), we must do one of two things. It will be instructive if you
learn BOTH ways.
Method 1. Reinterpret the problem as a "fewer than or equal to" problem this
way:
It is reported that in the Congress, 40% are NOT in favor of the Death
Penalty Law. If a group of 10 congressmen is chosen at random, find the
probability that 2 or fewer are NOT in favor of the Death Penalty Law.Think about it! That is the exact same problem! And it will have the same
answer.
To do it this way, on your TI-84, press 2ND VARS
Use the down arrow key to highlight B:binomcdf(
Press ENTER
If you see this, make it read:
binomcdf
trials:10
p:0.4
x value:2
Paste
Use the down arrow key to highlight Paste
Press ENTER
You will see:
binomcdf(10,0.4,2)
Press ENTER
You will see a decimal value. I won't tell you what it is, so you'll
have to do it yourself.
---OR--
Method 2. Find the complement event which is a "fewer than or equal to"
problem, then subtract from 1.
The complement event is:find the probability that 7 or fewer are in favor of the Death Penalty Law.
On your TI-84, press 2ND VARS
Use the down arrow key to highlight B:binomcdf(
Press ENTER
If you see this, make it read:
binomcdf
trials:10
p:0.6
x value:7
Paste
Use the down arrow key to highlight Paste
Press ENTER
You will see:
binomcdf(10,0.6,7)
You will see a decimal value. I won't tell you what it is, so you'll
have to do it yourself.
But that is the answer to to COMPLEMENT event problem, but NOT the answer
to your problem. To get the answer to your problem you must subtract that value from 1.
Then you will get the same answer as Method 1.
Edwin
