DAT questions help!

[savvysearch]

Hi, I have some questions I need help on. thanks in advance!

1) A person travels to work at an average speed of 40mph, and returns home at 60mph. Which of the following, in mph, is the average speed for the entire trip?

a)40 b)46 c)48 d)52 e)54

I can't figure that one out. The answer is C)48 but the only way I can think of solving it is to average the the speeds and get 50, which is wrong.

2)If 2x-3 > 3x+7, which of the following is true?

a)x>4/5 b)x>-4 c)x>-10 d)x<-4 e)x<-10

The answer is A. I completely forgot how to do these questions other than filling in x with the numbers. There must be a faster, more methodical way?

3) A mother's age is 3 times her daughter's age. In 12 years the mother's age will be twice the daugther's age at that time. How old is the mother now?

A)18 B)20 C)24 D)30 E)36

the answer is E.

4)A bowl contains 7 greens and 3 red marbles. what is the probability that 2 marbles selected at random from this bowl without replacement are both red.

A)1/15 b)9/100 c)21/100 d)47/90 e)6/10

answer is A

5)What is the variance of these set of numbers: (3,6,9,18)
a)31.5 b)10.5 c)7.4 d)27.5

answer is A.

6) how many feet are in a yard?

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[Pre-Dent-David]

3. y = 3x

y + 12 = 2x

3x + 12 = 2x

x = -12 I guess but you know its positive so there is your 36.




Maybe tomorrow I can help on more if nobody else does. Sorry but math is not my best subject. I fell your pain.

 

[Pre-Dent-David]

Ok for the marble one the first probability is 3/10 the second one is 2/9 .. Multiply these numbers. That is the math that I derived from the answer you provided.

 

[Pre-Dent-David]

I dont know about the inequality I got E. So Im lost.

 

[Pre-Dent-David]

I think 1 might need some calculus. .... hehe

 

[juan7677]

1) distance = rate x time (knowing this, set values for variables)
d = 120 mi (just made it up)
r1 = 40 mph (given), r2= 60 mph
t1 = ?, t2 = ? (you need to solve the time going there and coming back)
120 = 40 x t1 ==> t1 = 3
120 = 60 x t2 ==> t2 = 2
Total Time (T)= 3 + 2 = 5

D(total distance) = R (final rate) x T (total time)
240 = R x 5
R = 48!!!

2) I think the answer is wrong for this one. I got E.

 

[GV Black Jr.]

A dental student checking in.

There is a possibility that the first question is a printing error on the test. People do make mistakes. From the info you gave it would be 50mph.

Question 2 - You are right about answer and I do them the same we you do. I forget the "technical" method

Question 3 - I'm not sure the "technical" method but you are right

Question 4 - the probabilities of each individual event must be multiplied together. The first drawing is 3/10 chance and the second is 2/9 chance. 0.3 * 0.222222 = 0.066 is probability of both drawings being red. 1/0.066 = 15

Question 5 -

Question 6 - 3 feet or 36 inches

Sorry I couldn't be more help

GV Black jr.

 

[juan7677]

The first question is not an error, as GV Black suggested. The answer is C. You can't simply take the average of 40 and 60 mph b/c the time going to work and the time coming back is different.

 

[savvysearch]

thanks for the help. the answer for number 2 actually is E not A.

All I need is the answer to the 5 and Ill be set.

 

[dragonj]

to get variance you need the mean squared distance from the mean. which breaks down in the following way:

1. get the mean of your sample (18+9+6+3)/4=9

2. subtract each original number from your mean
9-18= -9
9- 9= 0
9- 6= 3
9- 3= 6

3. take these distances from mean and square each
-9*-9= 81
0* 0= 0
3* 3= 9
6* 6= 36
4. add these squares and get their mean
(81+0+9+36)/4=31.5

answer is 31.5

dragonj

 

[Pre-Dent-David]

Good job dragon.... I coulda have helped had i had my psych text book, but no such luck. back at the old dorm ha.

 

[savvysearch]

thanks a lot!