The Laws of Probability The Laws of Probability As They Pertain To As They Pertain To

GeneticsGenetics

P = F/TP = F/T

The probability of any event is The probability of any event is the quotient of the favorable the quotient of the favorable outcomes divided by the total outcomes divided by the total number of possible outcomesnumber of possible outcomes

P = 4 aces/52 cards =1/13P = 4 aces/52 cards =1/13

What is the probability of What is the probability of drawing an ace from a deck of drawing an ace from a deck of regular playing cards with one regular playing cards with one

blind draw?blind draw?

The probability of an event The probability of an event sure not to happen is zerosure not to happen is zero

What is the probability of What is the probability of throwing a seven (7) with throwing a seven (7) with one toss of a regular die?one toss of a regular die?

Zero!Zero!It is certain not to happen It is certain not to happen

because there is no 7 on the because there is no 7 on the diedie

P = 0/6 = 0P = 0/6 = 0

The probability of an event The probability of an event sure to happen is one (1)sure to happen is one (1)

What is the probability of a What is the probability of a steel shot hitting the steel shot hitting the

surface below it when it is surface below it when it is released?released?

One!One!Because of the law of Because of the law of gravity it is certain to gravity it is certain to

happen.happen.

The probability of The probability of simultaneous events is the simultaneous events is the product of their individual product of their individual

probabilities.probabilities.

(AND)(AND)

Toss a pair of dice. What is Toss a pair of dice. What is the P of throwing a six on the P of throwing a six on

one while throwing a six on one while throwing a six on the other?the other?

P = F/T X F/T P = F/T X F/T

The P of one 6 is 1/6 and The P of one 6 is 1/6 and the P of the other 6 is 1/6. the P of the other 6 is 1/6.

The P of simultaneous The P of simultaneous events (occurring at the events (occurring at the

same time) is 1/6 X 1/6, or same time) is 1/6 X 1/6, or 1/36.1/36.

The probability of mutually The probability of mutually exclusive events is the sum exclusive events is the sum

of their individual of their individual probabilitiesprobabilities

(OR)(OR)

Flip a penny. What is the P Flip a penny. What is the P you will get a heads or a you will get a heads or a

tails?tails?

If you flip a heads, you can’t If you flip a heads, you can’t get a tails. If you flip a tails, get a tails. If you flip a tails,

that eliminates the that eliminates the possibility of a heads. You possibility of a heads. You have mutually exclusive have mutually exclusive

events. So…………events. So…………

P = F/T + F/TP = F/T + F/T

P = ½ + ½ = 1P = ½ + ½ = 1

++

The probability of an event The probability of an event is not affected by previous is not affected by previous

outcomesoutcomes

After these results, what is After these results, what is the P of flipping heads on the P of flipping heads on

the next toss?the next toss?

? ?

P = F/T = ½P = F/T = ½

Previous outcomes have no Previous outcomes have no effect on the next toss!effect on the next toss!

¼ is the same as¼ is the same as

1:31:3 0.250.25 25%25%

How?

¼ means the same as 1 ¼ means the same as 1 favorable result to 3 favorable result to 3

unfavorable results…… 1:3unfavorable results…… 1:3

¼ means 1 divided by four ¼ means 1 divided by four which is 0.25which is 0.25

¼ means 0.25, which is ¼ means 0.25, which is read 25/100 which is 25%read 25/100 which is 25%

0.25 X 100% = 25%0.25 X 100% = 25%

With one draw from the deck With one draw from the deck what is the P of drawing:what is the P of drawing:

A 5?A 5? A heart?A heart? A 5 or a 7?A 5 or a 7? An ace and a heart?An ace and a heart? A face card?A face card?

Each of us puts our first Each of us puts our first name on a slip of paper and name on a slip of paper and places it in a can. We draw places it in a can. We draw one name. What is the P one name. What is the P

that it will be a girl’s name? that it will be a girl’s name? What is the P that it will What is the P that it will start with the letter R?start with the letter R?

With one toss of a pair of dice, With one toss of a pair of dice, what is the P of getting:what is the P of getting:

Snake eyes?Snake eyes? A 7 or 11?A 7 or 11? An unlucky 13?An unlucky 13?

Toss 4 dice. What is the P of Toss 4 dice. What is the P of getting a 1 on each of them getting a 1 on each of them

(a total of 4)?(a total of 4)?

You still want to gamble?You still want to gamble?