TI-84 Plus CE field manual for IB Math
Binomial probabilities
Use the binomial pdf and cdf routines to find P(X=k) and range probabilities P(a≤X≤b).
If X∼B(20, 0.3), find P(X=5) and P(4≤X≤12).
For P(X=5): open the distribution menu with and scroll down to A: binompdf(. Fill in trials: 20, p: 0.3, x value: 5, then highlight Paste and press . binompdf(20,0.3,5) pastes onto the home screen. Press again to evaluate it.
For P(4≤X≤12): binomcdf gives P(X≤x), so take the difference of two calls. Open and scroll down to B: binomcdf(. Fill in the upper bound (trials: 20, p: 0.3, x value: 12) and Paste. binomcdf(20,0.3,12) lands on the home screen. Press (the subtraction key), then open again and choose B: binomcdf( a second time, this time with x value: 3. With both calls on the home screen, press to evaluate.
Subtracting at 3 (not 4) keeps X=4 inside the range: P(X≤12)−P(X≤3) counts everything from X=4 up.
P(X=5)≈0.179 and P(4≤X≤12)≈0.892.
Your turn
Work each one on your calculator, then check the answer.
- 1
If X∼B(15,0.4), find P(X=6) and P(5≤X≤9).
- 2
If X∼B(25,0.2), find P(X=4) and P(3≤X≤8).
- 3
If X∼B(30,0.6), find P(X=18) and P(15≤X≤22).