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by stephny » Mon Nov 11, 2013 3:30 am
I cant seem to get these probability questions right,

pls someone help with this and also first steps to look out for when answering such questions:

WINK INc follows a certain procedure that requires two tasks to be finished independently in order for a job to be done. on a given day, there is a 7/8 probability that task1 will be completed on time, and a 3/5 probability that task2 will be completed on time. on acertain day, what is the probability that task1 will be completed on time but task2 will not?
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by theCodeToGMAT » Mon Nov 11, 2013 4:49 am
Task 1 completion probability = 7/8

Task 2 completion probability = 3/5

To find: probability that task1 will be completed on time but task2 will not

Task 1 Yes & Task 2 No

(7/8) * (1 - 3/5) = 7/8 * 2/5 = 7/20
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by Brent@GMATPrepNow » Mon Nov 11, 2013 8:18 am
stephny wrote: WINK INc follows a certain procedure that requires two tasks to be finished independently in order for a job to be done. on a given day, there is a 7/8 probability that task1 will be completed on time, and a 3/5 probability that task2 will be completed on time. on a certain day, what is the probability that task1 will be completed on time but task2 will not?
Complement rule: P(Event A not happening) = 1 - P(Event A happening)

Given:
P(task 1 completed on time) = 7/8
P(task 2 completed on time) = 3/5
P(task 2 not completed on time) = 1 - 3/5 = 2/5 [by the Complement rule]

P(task 1 on time AND task 2 not on time) = P(task 1 on time) x P(task 2 not on time)
= 7/8 x 2/5
= [spoiler]7/20[/spoiler]

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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