Some MATH questions ask for help!

[pojangchang]

All from [tooltip=Official Guide]OG[/tooltip]---but I still can't figure them out!!!!!

351.If the sum of n consecutive integers is 0, which of the following must be true?

I. n is an even number

II. n is an odd number

III. The average(arithmetic mean) of the n intergers is 0

(A)I only

(B)II only

©III only

(D)I and III

(E)II and III

A):E

 

352.In the formula V=1/(2r)^3, if r is halved, then V is multipled by

(A)64

(B)8

©1

(D)1/8

(E)1/64

A):B

 

362. 38, 69,22,73,31,47, 13, 82

Which of the following numbers is greater than three-fourths of the numobers but less than one-fourth of the numbers in the list above?

(A)56

(B)68

©69

(D)71

(E)73

A)

 

379. An arithmetic sequence is a sequence in which each term after the first is equal to the sum of the preceeding term and a constant. If the list of numbers shown above is an arithmetic sequence, which of the following must also be an arithmetic sequence?

I.2p, 2r, 2s, 2t, 2u

II.p-3, r-3, s-3, t-3, u-3

III.p^2, r^2,s^2,t^2,u^2

(A)I only

(B)II only

©III only

(D)I and II

(E)II and III

A)

 

438.Which of the following CANNOT be the median of the 3 positive integers x,y, and z?

(A)x

(B)z

©x+z

(D)x+z/2

(E)x+z/3

[neeraj.d]

Hi pojanchang,

 

351.

 

you see the sum has to be zero.. this means that half of the consecutive integers in the sequence are -ve and half +ve that gives us total integers to be even.. but zero will always be there in such sequence of consecutive integers, right.... that makes total no of integers to be odd .hence n will always be odd.

for ex. lets take the -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5

total nos =n= 11 right

and sum = 0

agaian the average of this sequence will be 0, as total -ve sum will cancel out total +ve sum.

hence the answer is (E)

 

362. here arrange the nos in increasing order....

13 22 31 38 47 69 73 83

in all total 8 nos.

now the no which is greater than 3/4 of the total nos mean and less than 1/4 of the total nos.

that means the no has to be greater than 3/4= 6/8 -> 6 out of 8 nos. i.e 13 22 31 38 47 and 69 and less than 1/4= 2/8= -> 2out of eight nos. i.e 73 and 83. only no that satisfy the condition is 71 .hence (D)

 

379.

I option If P Q R S T are in sequence than the sequence of twice the nos will also be in sequence coz the common differnce will also become twice in the new sequenc.. .. simply plug in the nos ...

 

II option will also bein sequence as the constant 3 is subtracted from all the nos , making it a sequence again. please verify by plugging in nos.

 

so answer is (D)

 

please tell me if i m worng and also the correct answers !!!!!!!!

 

hope this helps !!!!

 

Neeraj.

 

 

 

[www]

352

Try plugging in

Let's say r=2

V=1/8*2^3=1/64

when r is halved

V=1/8*1^3=1/8

Now 1/64*X=1/8

x=8