MGMAT problem

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HPengineer: Master | Next Rank: 500 Posts; Posts: 165; Joined: Wed Mar 24, 2010 8:02 amFollowed by: 1 member; Thanked: 2 times

by HPengineer » Sat Aug 28, 2010 4:49 pm

I thought i had a probabilities but lately i have been messing them up... Im multiplying when i should add and adding when i should multiply.... Did anyone face this problem before? Any suggestions on how to approach this?

Is the probability that Patty will answer all of the questions on her chemistry exam correctly greater than 50%?

(1) For each question on the chemistry exam, Patty has a 90% chance of answering the question correctly.

(2) There are fewer than 10 questions on Patty's chemistry exam.

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Source: Beat The GMAT — Data Sufficiency | Sat Aug 28, 2010 4:49 pm

pradeepkaushal9518: Legendary Member; Posts: 1309; Joined: Wed Mar 17, 2010 11:41 pmFollowed by: 5 members; Thanked: 33 times

by pradeepkaushal9518 » Sat Aug 28, 2010 9:56 pm

1.not sufficient
2.not sufficient

combine 1 and 2

i think we can solve imo C

A SMALL TOWN GUY

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sirisha.g: Senior | Next Rank: 100 Posts; Posts: 85; Joined: Thu Jul 15, 2010 7:50 pm; Thanked: 1 times; GMAT Score:690

by sirisha.g » Sat Aug 28, 2010 11:24 pm

IMO E. because as told by pradeep, A and B are not individually sufficient.

Now consider both the statements together. fewer than 10 implies questions can be 1 to 9
if you consider 1 question probability =0.9>0.5 hence YES
if you consider 8 questions probability=(0.9)^8=(0.9^2)^4=(0.8)^4 =0.4096<0.5 hence NO.

so insufficient. i arrived at this because the product of two decimal numbers will decrease and not increase.

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pradeepkaushal9518: Legendary Member; Posts: 1309; Joined: Wed Mar 17, 2010 11:41 pmFollowed by: 5 members; Thanked: 33 times

by pradeepkaushal9518 » Sat Aug 28, 2010 11:28 pm

srisha i think u r correct i was confused for fewer than 10

A SMALL TOWN GUY

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