HARDEST MATH IIc QUESTION! HELP!

Test Preparation
1

<p>Help!</p>

<p>The probability of passing a math test for Linda is 80%, the probability of passing a math test for Tom is 75%, and the probability of passing a math test for Alice is 60%. The probability of passing a math test for other seven students is 70%. If a teacher randomly picks two out of these ten students to take a math test, what is the probability that both students will pass the math test (assuming 75% means passing)?</p>

<p>???????????????</p>

2

<p>I probably did this wrong.. but is it 20%?</p>

3

<p>the probability of you getting an 800 on math 2c is 0%</p>

<p>lol ive met lots of people and puddinggirl had it coming.</p>

4

<p>i thot it would be 1/225</p>

5

<p>I thought 1/45</p>

6

<p>the probability is .497</p>

7

<p>I don't have a calc with me but the chances will be very high. assume the chances of the people are all 70% each. The possibility is close to 50%</p>

<p>EDIT: HAHA PIMP WAS 2 sec in front of me ^_^</p>

8

<p>There may be a quicker way to do this, but here's one possibility:</p>

<p>Evaluate all the possible pairs, and compute (probability of picking that pair).(probability that both in that pair will pass). All possible pairs are</p>

<p>Pair Prob(pick) x Prob(Both pass)
LT (1/10)(1/9)(0.8)(0.75)
LA (1/10)(1/9)(0.8)(0.6)<br>
LO (1/10)(7/9)(0.8)(0.7) </p>

<p>TL (1/10)(1/9)(0.75)(0.8)
TA (1/10)(1/9)(0.75)(0.6)<br>
TO (1/10)(7/9)(0.75)(0.7) </p>

<p>AL (1/10)(1/9)(0.6)(0.8)
AT (1/10)(1/9)(0.6)(0.75)<br>
AO (1/10)(7/9)(0.6)(0.7) </p>

<p>OL (7/10)(1/9)(0.7)(0.8)
OT (7/10)(1/9)(0.7)(0.75)<br>
OA (7/10)(1/9)(0.7)(0.6)<br>
OO (7/10)(6/9)(0.7)(0.7) </p>

<p>Now add up all the values in the last column, that should be your answer.</p>

9

<p>I got .467 also (rounded). What is the answer in the book (and what book is it)?</p>

10

<p>stix how did you get that??</p>

11

<p>Do the math in post#8, the numbers add up to 0.49677, which is consistent with post#6.</p>

12

<p>That is a good explanation. You can also just find the average probability of passing the test, and square it since there are two people.</p>

<p>(.705)^2 = .497025</p>

13

<p>Average the chances. Between 65-75. Then times 0.65-0.75 by itself to get the final answer. Certainly not one of the hard questions in 2c</p>