Official Quant thread for CAT 2013

@Narci said:
33 ?
no OA is D
@Pradeep_Rss said:
Mr x has 3 varieties of rice ie 15 rs ,18 rs ,22 rs per kg.he mixes it and sells at 22 rs a kg and gains 10 % profit. if he mixes 4 kg of 1st variety what is the diffrence between amount of 2 nd and 3 rd variety.help me out without taking X ..... thanks in advance.
I am getting the difference as 10... solved using alligation... What is the OA?
@albiesriram said:
m+n=33
or m=n=-33

35 solutions??
@ankitpurohit991 said:
I am getting the difference as 10... solved using alligation... What is the OA?
could u explain it?
@The_Loser said:
For how many natural numbers, N the expression N ˛ + N + 1 results in a perfect square?
0 ?
My explanation if I am right:

Least perfect square would be (N + 1)^2 and on expanding it needs N^2 + 2N + 1 which will never be possible.
@chintu61 said:
prime number is always odd except 2 ,( odd^4 = odd )+ (15*odd^2=odd) , so finally odd+odd-1=even, vch will be never a prime !! so "0" values, check for p=2, its value is even 75 vch isn't prime
bhai (odd + odd - 1) != even
odd + odd is even
@Pradeep_Rss
Rs 22 is the SP, so CP=Rs 20 (10%profit)
mix 1st 2 varieties..
15............?? .......................18
|_________|______________|
4kg......................................xkg
apply alligation-> we get ??=15+(3x/4+x)
now it is the same case as mixing (x+4)kg of another variety whose price is Rs15+(3x/4+x) with the 3rd variety of Rs 22 such that the resulting mixture is of Rs 20...
15+(3x/4+x)...........20 .................22
|________________|____________|
(x+4)kg .........................................ykg
applying alligation....
y/x+4= (20-15+(3x/4+x))/2
solve... u'll get y-x=10
@Logrhythm said:
m+n=33
or m=n=-33

35 solutions??
bhai iska solution post karo na
@Dexian said:
bhai iska solution post karo na
bhai just use a^3+b^3+c^3 - 3abc

where a=m, b=n and c=33
@Dexian said:
bhai iska solution post karo na
We know that a³ + b³ + c³ = 3abc, if a + b + c = 0 and vice-versa

Since here, m³ + n³ + (-33)³ = 3*m*n*(-33)
=> m + n - 33 = 0
=> m + n = 33

Since, mn 0 we can say that there will be 35 ordered pairs of (m, n)
@chillfactor please solve this question
@chillfactor Sir kindly help me be clear with a concept.

3x + 2y + z = 15

how do i find the positive integral solutions, non negative integral solutions and integral solutions of this question?

@Logrhythm said:
bhai just use a^3+b^3+c^3 - 3abc where a=m, b=n and c=33
can u please tell me how 35 solutions are there???

m+n=33
m can vary from 1- 32 ?????
@yudh said:
canu please tell me how 35 solutions are there???m+n=33m can vary from 1- 32 ?????
solve m+n=33,
34C1 soluntions for m+n=33, + 1 for m=n=-33
@iLoveTorres said:
@chillfactor Sir kindly help me be clear with a concept.3x + 2y + z = 15how do i find the positive integral solutions, non negative integral solutions and integral solutions of this question?
positive solutions=6
non negative solutions=17 ?

In a right angle triangle PQR , QS is an altitude to PR, /_PQR=90 , PS=16 cm , SR=4 cm , QS=?

@pankaj1988 said:
In a right angle triangle PQR , QS is an altitude to PR, /_PQR=90 , PS=16 cm , SR=4 cm , QS=?
8

@yudh

given: ax+by =7................(i)
ax2 + by2 = 49..................(ii)
ax3 +by3 = 133................(iii)
ax4 +by4 = 406................(iv)

to find: 2002(x+y +xy) + (a+b)/21

.

.

from (i) and (ii) we get b= 7(x-7)/(xy - y^2) ........(v)

from(ii) and (iii) we get b = 7(7x-19)/(xy^2 - y^3).....(vi)

from(iii) and (iv) we get b = 7(19x-58)/(xy^3 - y^4)....(vii)

.

.

equating the values of b derived above we get

.

(x-7) = (7x-19)/y = (19x-58)/y^2.................(viii)

.

=>(x-7)*(19x-58)/y^2 = (7x-19)^2/y^2 [multiply the LHS and RHS = square the middle]

=>(x-7)(19x-58) = (7x - 19)^2

=>x= 3 or x = -0.5

.

put x = 3 in (viii) to get

(3-7) = (7*3 - 19)/y

=>y= -0.5

so we put x=-0.5 and y=3 in (i) and (ii) to get

.

-0.5a+3b = 7

0.25a+9b = 49

=>21b = 63

=>b= 5 => a = 16

.

hence 2002(x+y+xy) + (a+b)/21 = 2002*(-0.5 +3 -0.5*3) + (16+5)/12 = 1

.

.

PS: COrrected for some calc. error.

ATDH.


@albiesriram said:
b)1