AP Statistics : How to use the multiplication rule

Study concepts, example questions & explanations for AP Statistics

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Example Questions

Example Question #31 : Probability

Charlene has 7 blue chips, and Karen has 5 green ones. They decide to mix them up in a bag, then Karen will pick 5 chips and Charlene gets the rest.

 

What is the likelyhood Karen ends up with 5 chips of the same color?

 

Possible Answers:

Correct answer:

Explanation:

There are 2 ways Karen gets 5 chips of the same color: she gets all 5 greens, or 5 blues. there is only 1 way to get all 5 greens: probability of which can be calculated as;

to calculate p(allblue) we use:

since order doesn't matter and chips are being drawn without replacement, this is an acceptable calculation and summing them yields 

Example Question #32 : Probability

A ninja is training for his super secret mission, throwing grappling hooks at targets ft away. He has determined over the last practice session, that he makes his shot roughly % of the time. What is the maximum number of shots the ninja will need to take to have a % chance of hooking his grapnel?

Possible Answers:

Correct answer:

Explanation:

Total likelihood of making the shot = sum of likelihood of making 1st shot+2nd shot+...

1st shot=

2nd shot=.

3rd shot=

4th=

5th=

6th=

Example Question #33 : Probability

Frank of the forest is a monkey man who was raised by chimpanzees from a very young age. He enjoys swinging with his monkey friends. When Frank jumps from one tree to another, the chance that he falls increases by 10% for every foot he jumps past his armspan of 3 feet. (he has a 10% chance of falling at 4ft)

One day, Frank watches his monkey friends do  jumps, one ft, one ft, another ft, one ft, a ft jump, another two ft jumps, and then a ft jump

Frank knows from experience not to take a jump route if the likelihood of him falling goes above %. At what point in this -jump route should Frank stop and rest?

Possible Answers:

Frank can finish this route, none of the jumps have above a % chance of falling

After  jumps, before the two ft jumps

After  jumps, before the ft jump

After  jumps, before the last ft jump

After  jumps, before the ft leap

Correct answer:

After  jumps, before the last ft jump

Explanation:

This is multiplication rule. let's calculate the chance frank doesn't fall.

For the first jump this is , the first two is , first 3: , first 4:, first 5:, first 6:, first 7:.

Since the 7th jump drops his survival rate below % (his fall rate above 60%) we would caution Frank to stop after his 6th jump, even if the 7th jump isn't that far

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