BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Probability and rate

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Newbie | Next Rank: 10 Posts
Posts: 3
Joined: Sun Oct 14, 2007 4:32 am

Probability and rate

by eririn » Wed Nov 28, 2007 5:34 pm
:)
A basket contains 5 apples, of which 1 is spoiled and the rest are good. If Henry is to select 2 apples from the basket simultaneously and at random, what is the probability that the 2 apples selected will incluede the spoiled apple?

A. 1/5
B. 3/10
C. 2/5
D. 1/2
E. 3/5

Ans. C

:(
Suzan drove at an average speed of 30 miles per hour for the first 30 miles of a trip and then at an average speed of 60 miles per hour for the remaining 30 miles of the trip. If she made no stops during the trip, what was Susan's average speed, in miles per hour, for the entire trip?

A. 35
B. 40
C. 45
D. 50
E. 55

Ans. B
Top
Source: — Problem Solving |
Senior | Next Rank: 100 Posts
Posts: 46
Joined: Fri Nov 23, 2007 1:36 pm

by syv11 » Wed Nov 28, 2007 6:54 pm
Question 1:

Probability of bad apple: 1/5. Simultaneously: 1/5+1/5=2/5

Question 2:

Suzan drove at an average speed of 30 miles per hour for the first 30 miles of a trip and then at an average speed of 60 miles per hour for the remaining 30 miles of the trip. If she made no stops during the trip, what was Susan's average speed, in miles per hour, for the entire trip?

first 30 miles at 30mph ===> 1h
second 30 miles at 60mph ===> 30m/60mph==>0.5h

Total distance 60 miles
time 1.h
average speed 40mph
Top
Legendary Member
Posts: 645
Joined: Wed Sep 05, 2007 4:37 am
Location: India
Thanked: 34 times
Followed by:5 members

by camitava » Wed Nov 28, 2007 11:19 pm
For second Qs, I agree with the approach which syv11 has taken.
But for 1, I am having some different approach - u can say -
We can take 2 apples out of 5 in 5C2 = 10 ways
Now 1 of the selected apple should be rotten and it can chosen in only 1 way.
The rest one apple can be chosen in = (5 - 1) = 4 ways
So total favorable oppurtunity = 4 + 1 = 5
So probability = 5 / 10 = 1/2. So IMO - D.
Now guys I am getting confused where I am wrong? But I can ask syv11 (Pls dnt mind) when u r taking 1/5 for the good apple - it will also the rotten apple also. Guys more input reqd. here.
Correct me If I am wrong


Regards,

Amitava
Top
Junior | Next Rank: 30 Posts
Posts: 14
Joined: Sun Dec 03, 2006 2:45 pm

by projase » Thu Nov 29, 2007 7:35 am
camitava wrote:For second Qs, I agree with the approach which syv11 has taken.
But for 1, I am having some different approach - u can say -
We can take 2 apples out of 5 in 5C2 = 10 ways
Now 1 of the selected apple should be rotten and it can chosen in only 1 way.
The rest one apple can be chosen in = (5 - 1) = 4 ways
So total favorable oppurtunity = 4 + 1 = 5
So probability = 5 / 10 = 1/2. So IMO - D.
Now guys I am getting confused where I am wrong? But I can ask syv11 (Pls dnt mind) when u r taking 1/5 for the good apple - it will also the rotten apple also. Guys more input reqd. here.
For me the easiest way to solve this is the following:

You can choose the bad apple either the first time or the sencond time.
The probailities to choose the bad the first time are 1/5.
The probailities to choose it the second time are = No First and Yes Second = 4/5 x 1/4 = 1/5.
So 1/5+1/5 = 2/5
Where there's a will, there's a way...
Top
Post new topic Post Reply
• Page 1 of 1