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prob question.

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by gmatterss » Fri Mar 27, 2009 1:01 am
hey all


can you tell me how to solve this

tanya prepared 4 different letters to be sent to 4 different addresses. For each letter she prepared envelopes with right address. if the 4 letters are put into the 4 envelopes at random, what is the probability that only one letter will be put into the correct address envelope.

a) 1/24

b) 1/4


c) 1/8

d) 1/3

e) 3/8
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5 pieces of wood have an average length of 124cm and median of 140 cm. what is the max possible length of the shortest piece.

a) 90

b) 140

c) 110

d) 130

e) 100
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3) Amy's grade was 90th percentile of the 80 grades for her class. of the 100 grades from other class, 19 were higher than any and others lower. if no grade was same as amy, then amy's grade was what percentile of grades of two classes combined.

72

80

81

85

92


thanks

harsha
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Source: — Problem Solving |

Re: prob question.

by Vemuri » Fri Mar 27, 2009 2:39 am
1. B. Probability that only one letter will be put into the correct address envelope: 4 possibilities/16 overall possibilities 4/16 = 1/4
I am not very sure of my answer though)

2. E. Total length of the wood is 124 * 5 = 620. If average is 140, then the remaining 4 pieces total to 620-140=480. If the 2 pieces above the average are the same as 140, then the remaining wood size will be 200. Maximum size of the smallest piece is thus 100.

3. D. I had to do some approximation here. So, will wait to see explanation from others on their approach. Not sure my answer is correct.
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by gmatterss » Fri Mar 27, 2009 5:50 am
hey vemuri


for the first ans given is 1/3 and thanks for the second question...


third ans is 85th
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by rs2010 » Fri Mar 27, 2009 9:04 am
First:

Total ways= 4*3*2*1=24

Favorable cases

Lets say first goes to correct one- 1 way
Second goes to incorrect one ways- 2 ways ( 1 will be correct)
For third - 1 way for incorrect ( 1 will be correct)
Fourth will automatically go in incorrect one.

ways=1*2*1*1=2

Now all these letter will fight so to give them equal chance mutliply by 4
total ways=2*4=8 :lol:

P=8/24=1/3

You need to remember here that if one letter goes in incorrect env then other letter will also get affected by this.

2. Vemuri explained

3.

90%ile of 80 ie she is ahead of 72
19 are ahead of her in 100 so out of 180 total behind her

72+81=153/180 so %ile is closer to 85.
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