Probability and rate

eririn · Posted: Wed Nov 28, 2007 5:34 pm Post subject: Probability and rate

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

Sad

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

syv11 · Posted: Wed Nov 28, 2007 6:54 pm Post subject:

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

camitava · Posted: Wed Nov 28, 2007 11:19 pm Post subject:

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.

projase · Posted: Thu Nov 29, 2007 7:35 am Post subject: