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shwang
Average Member

USA
11 Posts

 Posted - 08/31/2007 :  16:59:41 4. A bag contains 3 red marbles and 4 blue marbles. What is the probability that you select one red marble and one blue if you reach in the bag and randomly grab two marbles?CHOICES: a) 1/2 b) 3/5 c) 2/3 d) 4/7 e) 5/8WHAT I DID: I thought the chance of picking a red marble would be 3/7 and the chance of picking a blue marble is 4/7. ShouldnĄŻt I multiply these two fractions to get 12/49? But that answer isnĄŻt in the answer choice. What am I doing wrong?5. If the letters Ą°SAT TESTĄ± are placed in a box, what is the probability that you randomly draw two TĄŻs from the box?CHOICES: a) 1/7 b) 2/7 c) 3/7 d) 1/4 e) 1/6WHAT I DID: There are three TĄŻs out of seven letters total. The chance that IĄŻd draw 2 TĄŻs out of 3 TĄŻs can be expressed as 2/3. So when I multiply 2/3 with 3/7 I get 2/7. Is b) the right choice?6. In a student class election, every student in the class votes for 2 of 4 candidates. The person receiving the greatest number of votes is elected president. If Candidate B was elected president in the election with the results shown, what is the minimum number of students in the class?A-44 votesB-n votesC-38 votesD-16 votesCHOICES: a) 46 b) 72 c) 95 d) 121 e) 144WHAT I DID: I donĄŻt know how to approach this problem. I know that people who voted for D (16 ppl) also voted for another person.

galactus
Advanced Member

USA
1464 Posts

 Posted - 08/31/2007 :  19:26:39 quote:Originally posted by shwang4. A bag contains 3 red marbles and 4 blue marbles. What is the probability that you select one red marble and one blue if you reach in the bag and randomly grab two marbles?CHOICES: a) 1/2 b) 3/5 c) 2/3 d) 4/7 e) 5/8WHAT I DID: I thought the chance of picking a red marble would be 3/7 and the chance of picking a blue marble is 4/7. ShouldnĄŻt I multiply these two fractions to get 12/49? But that answer isnĄŻt in the answer choice. What am I doing wrong?Remember, there's no replacement. You didn't account for that. When one marble is drawn there is one less in the bag. They can be drawn in 2 different ways, red first or blue first.2(3/7)(4/6)=4/7See?.
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