Hi Abdulla,

a = To reach the destination, first find out total number of ways.
b = Then find out the number of ways in a particular manner mentioned in the problem.

Probability = b/a problem solved

Not let us find a and b.

First a:

Alicia has to cross 3 south and 3 east blocks. And, she can do this in any order.

So we need to find in how many ways we can arrange 3 south and 3 east blocks.

a = 6 ! / (3! * 3!) = 20

Now find b:

She has already traveled 2 south block, so she needs to travel 1 south and 3 east block.

b= 4 ! / (1! * 3 !) = 4

probability = b/a = 4/20 = 1/5

Let me know if anything is not clear to you.

uttam.albela wrote:Hi Abdulla,

a = To reach the destination, first find out total number of ways.
b = Then find out the number of ways in a particular manner mentioned in the problem.

Probability = b/a problem solved

Not let us find a and b.

First a:

Alicia has to cross 3 south and 3 east blocks. And, she can do this in any order.

So we need to find in how many ways we can arrange 3 south and 3 east blocks.

a = 6 ! / (3! * 3!) = 20

Now find b:

She has already traveled 2 south block, so she needs to travel 1 south and 3 east block.

b= 4 ! / (1! * 3 !) = 4

probability = b/a = 4/20 = 1/5

Let me know if anything is not clear to you.

Thank you uttam.albela, it's clear now.

uttam.albela wrote:Hi Abdulla,

a = To reach the destination, first find out total number of ways.
b = Then find out the number of ways in a particular manner mentioned in the problem.

Probability = b/a problem solved

Not let us find a and b.

First a:

Alicia has to cross 3 south and 3 east blocks. And, she can do this in any order.

So we need to find in how many ways we can arrange 3 south and 3 east blocks.

a = 6 ! / (3! * 3!) = 20

Now find b:

She has already traveled 2 south block, so she needs to travel 1 south and 3 east block.

b= 4 ! / (1! * 3 !) = 4

probability = b/a = 4/20 = 1/5

Let me know if anything is not clear to you.

Hi Utam:

The question is the probaility of walking south the first 2 blocks, right? This means walking south the first block (a), and then walking south the second (b), that is:

P(a)*P(b)a = (3/6)*(2/5) = 6/30 = 1/5

Am I wrong?

Silvia

ssuarezo wrote:

uttam.albela wrote:Hi Abdulla,

a = To reach the destination, first find out total number of ways.
b = Then find out the number of ways in a particular manner mentioned in the problem.

Probability = b/a problem solved

Not let us find a and b.

First a:

Alicia has to cross 3 south and 3 east blocks. And, she can do this in any order.

So we need to find in how many ways we can arrange 3 south and 3 east blocks.

a = 6 ! / (3! * 3!) = 20

Now find b:

She has already traveled 2 south block, so she needs to travel 1 south and 3 east block.

b= 4 ! / (1! * 3 !) = 4

probability = b/a = 4/20 = 1/5

Let me know if anything is not clear to you.

Hi Utam:

The question is the probaility of walking south the first 2 blocks, right? This means walking south the first block (a), and then walking south the second (b), that is:

P(a)*P(b)a = (3/6)*(2/5) = 6/30 = 1/5

Am I wrong?

Silvia

Hi Silvia,

I liked your approach for getting the probability. Nice approach of getting probability of first south out of total 3 south and 3 east block and then get 2nd south out of 2 south and 3 east blocks.

My approach would have been good, if we needed to find only the number of ways of doing it. But for getting probability your approach is the best Thanks a lot !

I would go the MGMAT anagram way.

We know that without any restriction she has to go 3 blocks south and 3 blocks east to get to work
Hence,we need to find the number of arrangements of the anagram SSSEEE

Total arrangements : 6!/3!*3! = 20

We know that she has to take 2 blocks south 1st. So 1st 2 are fixed SS. The remaining 4 steps we will have to find the number of arrangements of SEEE
= 4!/3!*1! = 4

Hence PRobability = No of fav/total = 4/20 = 1/5