OG - On Saturday morning, Malachi will begin a

[fiza gupta]

On Saturday morning, Malachi will begin a camping vacation and he will return home at the end of the first day on which it rains. If on the first three days of the vacation the probability of rain on each day is 0.2, what is the probability that Malachi will return home at the end of the day on the following Monday?

A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

OA:B

[crackverbal]

Hi Fiza Gupta,

So as given in the question, we are looking for the probability of the following event NNR: no rain on first day, no rain on second day and rains on third day (Monday).

Given p(Rain) = 0.2

So p(Not Rain) = 0.8

P(NNR) = P(N) * P(N ) * P(R)

= 0.8 * 0.8 * 0.2

= 0.128

So the answer is B.

Hope this is clear.

[Brent@GMATPrepNow]

On Saturday morning, Malachi will begin a camping vacation and he will return home at
the end of the first day on which it rains. If on the first three days of the vacation the
probability of rain on each day is 0.2, what is the probability that Malachi will return
home at the end of the day on the following Monday?
A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

NOTE: if P(rain on a certain day) = 0.2, then we know that P(NO rain on a certain day) = 1 - 0.2 = 0.8

For probability questions, I always ask, "What needs to happen for the desired event to occur?"

For this question P(come home Monday night) = P(no rain on Saturday AND no rain on Sunday AND rain on Monday)

At this point, we can apply what we know about AND probabilities. We get:
P(come home Monday night) = P(no rain on Saturday) X P(no rain on Sunday) X P(rain on Monday)
= (0.8) X (0.8) X (0.2)
= 0.128
= B

RELATED VIDEOS
- Rewriting Questions: https://www.gmatprepnow.com/module/gmat ... /video/754
- Probability of Event A AND Event B: https://www.gmatprepnow.com/module/gmat ... /video/750
- The Complement: https://www.gmatprepnow.com/module/gmat ... /video/744

[DavidG@VeritasPrep]

On Saturday morning, Malachi will begin a camping vacation and he will return home at the end of the first day on which it rains. If on the first three days of the vacation the probability of rain on each day is 0.2, what is the probability that Malachi will return home at the end of the day on the following Monday?

A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

OA:B

You can also reason your way through using a little logic and the answer choices. .008 is way too small - that's the probability that it rains on all three days. (.2)^3. (But we only want it to rain on the last day.) So A is out. And note that .488 is too big, as the probability of rain on any given day is .2. If we're multiplying .2 by something less than 1, the answer will have to be less than .2. Well, the only answer choice greater than .008 and less than .2 is B.

[Scott@TargetTestPrep]

On Saturday morning, Malachi will begin a camping vacation and he will return home at the end of the first day on which it rains. If on the first three days of the vacation the probability of rain on each day is 0.2, what is the probability that Malachi will return home at the end of the day on the following Monday?

A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

OA:B

Since we need to determine the probability that Malachi will return home at the end of the day on the following Monday, we must determine:

P(no rain Sat and no rain Sun and rain Mon) = P(no rain Sat) x P(no rain Sun) x P(rain Mon)

Since the probability of rain is 0.2, the probability of no rain is 1 - 0.2 = 0.8, and thus:

P(no rain Sat) x P(no rain Sun) x P(rain Mon) = 0.8 x 0.8 x 0.2 = 0.128

Answer:B

[[email protected]]

Hi fiza gupta,

David's approach showcases how useful the answer choices can be in helping you to avoid longer, 'math heavy' approaches. On at least a couple of Quant questions on Test Day, the answer choices will be designed in such a way as to help you avoid long-winded math. You'll still have to take some notes and think critically about the information that you're given, but you'll be able to use those answers to get to the correct answer in less time and with less overall effort.

GMAT assassins aren't born, they're made,
Rich

[fiza gupta]

Thanku Experts

[hoppycat]

On Saturday morning, Malachi will begin a camping vacation and he will return home at the end of the first day on which it rains. If on the first three days of the vacation the probability of rain on each day is 0.2, what is the probability that Malachi will return home at the end of the day on the following Monday?

A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

OA:B

You can also reason your way through using a little logic and the answer choices. .008 is way too small - that's the probability that it rains on all three days. (.2)^3. (But we only want it to rain on the last day.) So A is out. And note that .488 is too big, as the probability of rain on any given day is .2. If we're multiplying .2 by something less than 1, the answer will have to be less than .2. Well, the only answer choice greater than .008 and less than .2 is B.

That's a huge timesaver. Is it common to have questions where you can just use logic and not solve the question?

[DavidG@VeritasPrep]

On Saturday morning, Malachi will begin a camping vacation and he will return home at the end of the first day on which it rains. If on the first three days of the vacation the probability of rain on each day is 0.2, what is the probability that Malachi will return home at the end of the day on the following Monday?

A. 0.008
B. 0.128
C. 0.488
D. 0.512
E. 0.640

OA:B

You can also reason your way through using a little logic and the answer choices. .008 is way too small - that's the probability that it rains on all three days. (.2)^3. (But we only want it to rain on the last day.) So A is out. And note that .488 is too big, as the probability of rain on any given day is .2. If we're multiplying .2 by something less than 1, the answer will have to be less than .2. Well, the only answer choice greater than .008 and less than .2 is B.

That's a huge timesaver. Is it common to have questions where you can just use logic and not solve the question?

It's common enough that you want to be in the habit of always giving the answer choices a once-over before you dive in and start doing any intensive arithmetic or algebra. Generally speaking, the further apart the answer choices are, the better the odds that reason and estimation alone will get you to the correct answer. A useful exercise is to go back to questions you were able to answer correctly in a formal way and see if you could have gotten there using a strategic shortcut. You'll be surprised at how often that would have been a viable option.

[Matt@VeritasPrep]

That's a huge timesaver. Is it common to have questions where you can just use logic and not solve the question?

Absolutely! The art of the best official questions is testing precisely this. (The idea: if you can see these sorts of shortcuts on a math test, you'll also see them in the business world, quantitative finance, real estate, wherever.)

[hoppycat]

That's a huge timesaver. Is it common to have questions where you can just use logic and not solve the question?

Absolutely! The art of the best official questions is testing precisely this. (The idea: if you can see these sorts of shortcuts on a math test, you'll also see them in the business world, quantitative finance, real estate, wherever.)

Any more tips like that ?

[Matt@VeritasPrep]

That's a huge timesaver. Is it common to have questions where you can just use logic and not solve the question?

Absolutely! The art of the best official questions is testing precisely this. (The idea: if you can see these sorts of shortcuts on a math test, you'll also see them in the business world, quantitative finance, real estate, wherever.)

Any more tips like that ?

Oh goodness, zillions. Can you give me a little more direction? I have so many, not sure where to begin.

[hoppycat]

That's a huge timesaver. Is it common to have questions where you can just use logic and not solve the question?

Absolutely! The art of the best official questions is testing precisely this. (The idea: if you can see these sorts of shortcuts on a math test, you'll also see them in the business world, quantitative finance, real estate, wherever.)

Any more tips like that ?

Oh goodness, zillions. Can you give me a little more direction? I have so many, not sure where to begin.

I'll take ANY time saving tips

[DavidG@VeritasPrep]

That's a huge timesaver. Is it common to have questions where you can just use logic and not solve the question?

Absolutely! The art of the best official questions is testing precisely this. (The idea: if you can see these sorts of shortcuts on a math test, you'll also see them in the business world, quantitative finance, real estate, wherever.)

Any more tips like that ?

Oh goodness, zillions. Can you give me a little more direction? I have so many, not sure where to begin.

I'll take ANY time saving tips

I wrote about a couple of my favorite here: https://www.veritasprep.com/blog/2015/0 ... -test-day/