NP, Ch4, Q3 - Page 65. There is a 30% chance of rain and a

[georgepa]

There is a 30% chance of rain and 70% chance of shine. If it rains, there is a 50% chance that Bob will cancel his picnic, but if the sun is shining, he will definitely have his picnic. What is the chance that Bob will have his picnic ?


I got the answer without using the formula but by charting. This is another way to do the problem

Since the days added up to a 100% I thought about the time in consideration as a span of 100 days.

Code: Select All Code

  Days with Rain    |  Days with Sunshine
       30           |       70
        |           |        |
  Picnic   NoPicnic |  Picnic  NoPicnic
   15         15    |   70       0


ANSWER:

Total # of days with picnic = 70 + 15 = 85

Therefore, there are 85 days when Bob can have a picnic out of a total of 100 days. So the chance that bob will have his picnic is 85%

Or using a Chart

Code: Select All Code

# Days | Picnic | No Picnic | Total
------------------------------------
Rains  |  15    |  15       |  30
------------------------------------
No Rain|  70    |  0        |  70
------------------------------------
Total  |  85    |  15          100


ANSWER:

Total # of days with picnic = 15 + 70 = 85

Therefore, there are 85 days when Bob can have a picnic out of a total of 100 days. So the chance that bob will have his picnic is 85%

[jyothi h]

There is a 30% chance of rain and 70% chance of shine. If it rains, there is a 50% chance that Bob will cancel his picnic, but if the sun is shining, he will definitely have his picnic. What is the chance that Bob will have his picnic ?


I got the answer without using the formula but by charting. This is another way to do the problem

Since the days added up to a 100% I thought about the time in consideration as a span of 100 days.

Code: Select All Code

  Days with Rain    |  Days with Sunshine
       30           |       70
        |           |        |
  Picnic   NoPicnic |  Picnic  NoPicnic
   15         15    |   70       0


Total # of days with picnic = 70 + 15 = 85


Or using a Chart

Code: Select All Code

# Days | Picnic | No Picnic | Total
------------------------------------
Rains  |  15    |  15       |  30
------------------------------------
No Rain|  70    |  0        |  70
------------------------------------
Total  |  85    |  15          100


----------------------------------------

Chance that bob will have his picnic =( 50% change if it rains) OR 100 % chance if the sun shines
= (3/10)*(1/2) + 7/10 = 17/20

Appreciate if you can post the answers too for the question.

Thanks,
Jyothi

[RonPurewal]

sure, that works. (to the original poster: you forgot to answer the actual question! you just stopped at the number of days.)

jyothi, most of the problems in the strategy guide don't have answer choices. i don't have the guide in front of me right now, but it's quite possible that this is one such problem.

[jyothi h]

sure, that works. (to the original poster: you forgot to answer the actual question! you just stopped at the number of days.)

jyothi, most of the problems in the strategy guide don't have answer choices. i don't have the guide in front of me right now, but it's quite possible that this is one such problem.

Oh Ok .I get it. I wasn't sure what I had done was right or not and wanted confirmation on that which I why I requested for an answer. But I see what you mean

Thanks,
Jyothi

[jlucero]

Glad it helped!

[georgepa]

@Ron. I thought I had the answer in the original post since my setup included the 100 days. Anyway, I've edited my original post to be much clearer.

[RonPurewal]

@Ron. I thought I had the answer in the original post since my setup included the 100 days. Anyway, I've edited my original post to be much clearer.

ok... and i've moved this thread to where it actually belongs in the first place, i.e., the non-CAT MGMAT forum.
please don't post non-GMATPREP stuff in the GMATPREP folder; thanks in advance.