Probability

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C: Junior | Next Rank: 30 Posts; Posts: 23; Joined: Mon Feb 08, 2010 8:19 am; Location: Norway; Thanked: 1 times

by C » Wed Apr 14, 2010 3:45 am

In the town of Z, the town lion roars on some days and not on others. If a day is chosen at random from last March, what is the probability that on that day, either the town lion roared or it rained?

(1) Last March, the lion never roared on a rainy day.

(2) Last March, the lion roared on 10 fewer days than it rained.

OA is E.

Source is MGMAT Word Translations. Can someone please solve and explain?

Thanks.

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Source: Beat The GMAT — Data Sufficiency | Wed Apr 14, 2010 3:45 am

ajith: Legendary Member; Posts: 1275; Joined: Thu Sep 21, 2006 11:13 pmFollowed by: 2 members; Location: Arabian Sea; Thanked: 125 times

by ajith » Wed Apr 14, 2010 4:10 am

C wrote:In the town of Z, the town lion roars on some days and not on others. If a day is chosen at random from last March, what is the probability that on that day, either the town lion roared or it rained?

(1) Last March, the lion never roared on a rainy day.

(2) Last March, the lion roared on 10 fewer days than it rained.

OA is E.

Source is MGMAT Word Translations. Can someone please solve and explain?

Thanks.

Say A is the set of all days in which it rained in March
B is the set of all days in which the lion roared in March

To answer the question we need to n(AâˆªB)

1) A and B are independent => n(AâˆªB) = n (A) + n(B)

Which is not sufficient

2) n(B) <10

Which is not sufficient

Combined also we cant fine n(AâˆªB)

Hence E

Always borrow money from a pessimist, he doesn't expect to be paid back.

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akhpad: Legendary Member; Posts: 809; Joined: Wed Mar 24, 2010 10:10 pmFollowed by: 4 members; Thanked: 50 times

by akhpad » Wed Apr 14, 2010 6:56 am

Some more explanation

https://www.beatthegmat.com/roar-and-rain-t55146.html

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