One name is drawn and replaced. A second name is drawn. What is the probability that both named drawn are girls' names?
A. 1/78
B. 42/121
C. 49/121
D. 49/16
Can someone explain how to get an equation out of all the mumbo jumbo? :S
2006-09-26 13:59:30 · 8 answers · asked by Madcat 2 in Science & Mathematics ➔ Mathematics
The probability of two independant events occuring is the probability of the first event times the probability of the second event.
event 1 is drawing a girls name.
event 2 is drawing a girls name
probability of event 1 = probability of event 2 = 7/11
because there are 7 girls names and 11 total names.
7/11 * 7/11 = 49/121
2006-09-26 14:04:07 · answer #1 · answered by Demiurge42 7 · 1⤊ 0⤋
Ok, i think the best way to approach this is to ask 'what is the probability of drawing a girl's name?'
Pgirl = 7 / 11 ( 7 girls names out of a total of 11 names)...
Now the question states that one name is drawn and then replaced and the second name is drawn.
This tells us 2 things: Firstly that the two events are independent (independent meaning that the first event's outcome does effect that second event's outcome)
The second thing that we know from the question is that since the first name is replaced, the odds/probability is the same of drawing a girls name the second time or 7 / 11.
When dealing with independent events and probabilities to find the 'overall' probability of a number of independent events, you multiply the probabilites together. The question asks, what is the probability that both drawings will be girls names.
Pbothgirls = Pgirlname1 * Pgirlname2
Pbothgirls = ( 7/ 11 * 7/11) , note: we know that the second probability is the same - 7 / 11 - because the first name drawn is replaced.
so Pbgirls = 49 / 121 or C.
Hope this helps...
Good luck.
2006-09-26 14:13:32 · answer #2 · answered by Mark B 2 · 1⤊ 0⤋
Its C.
7/11 times 7/11 gives you 49/121.
2006-09-26 17:53:01 · answer #3 · answered by crazy8tiger 4 · 1⤊ 0⤋
This is done by multiplying the fractions. Since their are 7 girls out of 11 kids, you multiply 7/11 by 7/11 to get 49/121
2006-09-26 14:14:17 · answer #4 · answered by Tori H 2 · 1⤊ 0⤋
the likelyhood that a girl is drawn is 7/11, seven girls out of 11 possibilities
the likelyhood that a girl is drawn the second time is 7/11, seven girls again out of 11 possibilities
to combine these separate occurances, multiply the fractions
7/11*7/11=(7*7)/(11*11)= C. 49/121
2006-09-26 14:05:01 · answer #5 · answered by Keith H 3 · 1⤊ 0⤋
The odds of drawing a girl's name are 7/11
once you replace the name you drew, you draw another one.
The odds of drawing a girl's name the second time are 7/11.
The odds of drawing a girls name both times can be found by
(7/11) * (7/11) = ____
The answer is 49/121
2006-09-26 14:21:54 · answer #6 · answered by Ricky 1 · 1⤊ 0⤋
the probability of the first draw is 7/11.
the probability of the second draw is independent of the first draw and is also 7/11.
The second is independent because it is not effected by the out come of the first draw.
the compoumd probability of independent events is just the product of the probibalitys of the events. in this case ---
7/11 X 7/11 = 49/121
2006-09-26 14:32:35 · answer #7 · answered by horse 2 · 1⤊ 0⤋
This is really easy.
You should learn it or you'll flunk the test. (sorry to be such a jerk, but you ARE going to take a test on this, right?)
2006-09-26 14:04:56 · answer #8 · answered by Jim S 5 · 0⤊ 1⤋