GMAT Math !Please help me to answer the GMAT questiones!Thx

[maypoon]

Dear all,

Please teach me how to deal with the following questiones!Thank you so much !

Q1. A certain roller has 3 cars, and a passenger is equally likely to ride in any 1 of the 3 cars each times that passenger rides the roller coaster. If a certain passenger is to ride the roller coaster 3 times, what is the probability that passenger will ride in each of the cars?

A. 0
B. 1/9
C. 2/9
D. 1/3
E. 1
Ans : C



Q.2 There 're 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks. How many possible selections of 4 books from this self include at least 1 paperback?

A. 40
B. 45
C. 50
D. 55
E. 60
Ans. C

Q3. In a corporation, 50 percent of the male employees and 40 percent of the female employees are at least 35 years old . If 42 percent of all the employees are at least 35 years old, what fraction of the employees in the corporation are females?

A. 3/5
B. 2/3
C. 3/4
D. 4/5
E. 5/6
Ans. D

Q4. In town X, 64% of the population are employed , and 48% of the population are employed males. What % of the employed people in town X are females?

A. 16%
B. 25%
C. 32%
D. 40%
E. 52%
Ans: B
(Why the answer isn't C)

Q5. How many integers from 0 to 50 , inclusive , have a reminder of 1 when divided by 3?

A. 15
B. 16
C. 17
D. 18
E. 19
Ans: C
(Why not B??)

[DanaJ]

Q1. The probability of picking one cart of the three possible is 1, since you have to pick one cart out of a number of three possible, but it doesn't matter which cart. Now, in order to pick another cart, you have a probability of 2/3, since there are two other carts to choose from (since you've already picked one of the three) out of a total of three. Now the third time the guy has only one cart left, since he's already ridden in the other two. The probability of picking this one is therefore 1/3. In the end you get total probability by multiplying the probabilities for the three cases: 1*2/3*1/3 = 2/9.
Answer C.

Q2. Selections of 4 books from this self with at least 1 paperback mean selections of 4 books with either 1 or 2 paperbacks.
Let's take the first case when you have 1 pb and 3 hb. Choosing 3 hb from a total of 6 hb makes for 6C3, which is 20. Now, since you've got 2 possible pb, this makes for 2*20 = 40 combinations with one pb.
When you have 2 pb and 2 hb, this is down to selecting the hb's, so the number of combinations will be 6C2 = 15.
Total number of combinations: 40 + 15 = 55, with answer D. Can you please double-check the answer? Although I admit I may be wrong... If I am, I'm really sorry...

Q3. Say m = male employees and f = female employees
This means that 50%*m + 40%*f = total employees over 35, which is 42% of the total (total = m + f). So you get that:
0.5m + 0.4f = 0.42(m + f) or 0.5m + 0.4f = 0.42m + 0.42f, or that 0.08m = 0.02f. This means that 8m = 2f or that 4m = f. So you get that the total number of employees is m + f = m + 4m = 5m. Now, the fraction of female employees will be 4m/5m = 4/5. Answer D.

Q4. Again, we have m = male population and f = female population. You get that 64% of total (which is m + f) are employed, while 48% of total are employed males. This means that 64 - 48 = 16% of total population are employed females. Now, they are asking what percent of the employed population are employed females. Well, since 64% of population are employed and 16% of population are employed females, the percentage will be 16/64 = 0.25 = 25% of employed women or one fourth. Answer B.

Q5. Let's start by counting the number of multiples of 3 from 0 to 50. You have 0, 3, ..., 48, so there are (48/3) + 1 = 16 + 1 = 17 multiples of 3 from 0 to 50. I think that that "+1" might confuse you: it's because we start from 0! Notice that there are 10 numbers from 1 to 10, but there are 11 numbers from 0 to 10 (you can easily verify that by using our God-given fingers :D ). So you are looking for numbers that have a remainder of 1 when divided by 3. There will be exactly 17 of them, since you have exactly 17 multiples of 3 between 0 and 50. The numbers will be: 1, 4, ..., 49, one number corresponding to each multiple of 3. Answer C.

[nattatob]

I strongly agree with the above reply:

1. 2/9 comes from 6/27

27 = total prop = 3x3x3
6 = tree cars factorial or 3!

2. I got choice D like her.

Total prop - Never paperback = (8!/4!4!) - (6!/4!2!)
= 55

3. 0.5M+0.4F = 0.42(M+F)
0.5M+0.4F = 0.42M+0.42F
0.08M = 0.02F
so 8M=2F
or F=4M
then, F/(M+F) = 4M/(M+4M) = 4M/5M
or 4/5 or 20%

4. 64% is total employed, but have 48% be male
so there are 48%=male and 16%=female
16%/64% = 1/4 = 25%

5. You forgot the one number = 1
Is 1/3 = 0.333 ?

[maypoon]

Dear all,

Thank you som much ! You have helped me a lots .....
I hope I can get a good result in GMAT!

Wishes you all the best in 2009!

Best Wishes,
May