HELP! Some QR Questions!!!!!!!!!!!!!!!!!!!!!!

[HC_smiles]

if anyone could explain the solutions to these i would be forever grateful:

1) since 1 meter = 3.28 ft, 2/3 foot equals approximately what fraction of a meter? answer = 1/5

2) if the side length of a square is increased by 50%, the area increases by what percent? ans = 125

3) Rich is 1/6 of his father's age. In 20 years he will be 1/2 of his father's age at that time. How old is his father now?
a. 24
b. 36
c. 30
d. 42
e. 38
ans according to barron is c, but doesnt a work out too????????

4) kate has 6 different books. assuming order of selection doesn't matter, how many ways can kate select, from these 6 books, two different books?
ans = 15

5) a bowl contains 7 blue and 3 red marbles. what is the probability that 2 marbles selected at random from this bowl without replacement are both red?
ans = 1/15

6) a gift of $180 is to be shared by brett and andrew such that andrew gets 25% more than brett. how much does brett get?
answer = e

**quickie question: what is variance in regards to finding the mean of a set of numbers? i know how to find mean, but kind of lost on variance


thanx so much!!!!!! back to studying i go....

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[mola_pulla]

1)
Just set these two parts equal to each other. 2/3=x(3.28) x being the fraction you are looking for. so the answer will be (2/3)(1/3.28)=1/5 or .20

2)
Not sure on this one.

3)
You can set this up if you know R=1/6F, and then set up the equation 20+(1/6)F=(1/2)(20 +F). R stands for Rich and F for his father. The left side of the equation is Rich's age in twenty years, and the right side is that rich will be one half his fathers age in twenty years. Just plug and chug now. THESE TYPES of QUESTIONS WILL BE ON THE DAT. They are on every practice one and on the DAT of all of my friends.

4)
look up the permutation rule on the internet or in a math book to learn this. The equation to use is 6!/(2!(6-2)!). This looks confusing but it is really an easy concept to grasp after reading about it. The ! means Factorial. so it really is (6*5*4*3*2*1)/((2*1)(4*3*2*1)).

5)
Times the two probabilities of getting each outcome together. You have 3 red marbles in a total of 10, so for the first marble the prob will be 3 out of 10 or 3/10, then without putting the marble back, your prob of taking another red marble is 2 out of 9, or 2/9. Times those two together and you get 1/15.

6)
Set up the equation, B is for brett and A for andrew, We know they are sharing $180 so B+A=180, B=x and A=(.25x+x), meaning Andrew gets 25% more. and plug them into the equation. x+(.25x+x)=180.


variance
After finding the mean of a group of numbers the variance is then calculated,
like the Standard deviation but you don't take the square root. Google this and it will give you the equation on the DAT these questions are usually simple numbers so don't get scared at the size of this equation.

Hope this helps. If you have any other questions or if this doesn't make sense then I'll try to help you out again.


20/20/19

 

[checkamundo]

1) since 1 meter = 3.28 ft, 2/3 foot equals approximately what fraction of a meter? answer = 1/5

Ans: Use the conversion factor given
(2/3 ft)(1 meter/3.28 ft) = 1/5

2) if the side length of a square is increased by 50%, the area increases by what percent? ans = 125

3) Rich is 1/6 of his father's age. In 20 years he will be 1/2 of his father's age at that time. How old is his father now?
a. 24
b. 36
c. 30
d. 42
e. 38
ans according to barron is c, but doesnt a work out too????????

Ans: r = (1/6)f and (r + 20) = (1/2)(f + 20) so solve for one letter and plug into other eqn and father= 30 and rich= 5



4) kate has 6 different books. assuming order of selection doesn't matter, how many ways can kate select, from these 6 books, two different books?
ans = 15

Ans: (6!) / (2!)(6-2)! = 15

5) a bowl contains 7 blue and 3 red marbles. what is the probability that 2 marbles selected at random from this bowl without replacement are both red?
ans = 1/15

Ans: (3/10)(2/9) = 1/15

6) a gift of $180 is to be shared by brett and andrew such that andrew gets 25% more than brett. how much does brett get?
answer = e

Ans: 180 = b + a and a = 1.25(b) so b =80 and a=100


**quickie question: what is variance in regards to finding the mean of a set of numbers? i know how to find mean, but kind of lost on variance

variance = ∑(x - b) / (n -1) where b = mean, n = total number of
observations

thanx so much!!!!!! back to studying i go.... [/QUOTE]

 

[midwestboy]

The variance and the closely-related standard deviation are measures of how spread out a distribution is. The variance is computed as the average squared deviation of each number from its mean. For example, for the numbers 1, 2, and 3, the mean is 2 and the variance is:

((1-2)^2+ (2-2)^2+ (3-2)^2)
s^2= ----------------------------- == 1
2

 

[lifeisgood]

if anyone could explain the solutions to these i would be forever grateful:

2) if the side length of a square is increased by 50%, the area increases by what percent? ans = 125
....

There are a few ways to do this problem...you can say

A1 = x^2

A2 = (3/2 x)^2 = 9/4 x^2

A2-A1 = 9/4 x^2 - x^2 = 5/4 x^2 = 125% x^2

Or you can say square 1 w/ side=4 then A1=16
Square 2 w/ side=6 then A2=36

A2-A1 = 20

20/16 = 5/4 = 125%

 

[HC_smiles]

YOU GUYS ARE ALL AWESOME!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! THANX A MILLION TIMES OVER!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[armorshell]

Yeah thanks guys, somehow in the huge span of my education I've never run into permutations before...I didn't even know what they were called