Official Quant thread for CAT 2013

@jain4444 said:
For how many positive integers n are there exactly ⌊n/2⌋ or ⌈n/2⌉ primes less than or equal to n ? ⌊⌋ = the largest integer less than or equal to x.⌈⌉ = the smallest integer greater than or equal to x.
for 1, we have 0 prime number...
for 2, we have 0
for 3, we have 1
4 we have 2...
for every odd number n+1/2 and n-1/2 are least integer greater than equal to and greatest integer less than equal to value of n/2
after a certain number, the number of prime numbers start decreasing,
for 5 we have 2
6 we have 3
7 we have 3
8 we have 4
9 we have 4
10 we have 4...
11 we have 4,,,
12 we have 5//
13 we have 5
so we have 1,3,4,5,6,7,8,9 as the numbers which satisfy as the value of n... 8 such numbers..
@gautam22 said:
not even close??
bhai kaise kiya hai...i m getting 4 gallons??

60 m/hr - 1 gallon - 20 miles
75 m/hr - 1 gallon - 70/100*20 = 14 miles
so...to cover 20 miles at 75 m/hr..it will consume = 20/14 gallons
75 m/hr ----> 20/14 gallons....for 20 miles
210 m/hr ----> 210*20/14*1/75 = 4 gallons
@albiesriram said:
2/3
@albiesriram said:
a point is picked... now any point when joined with this making a chord having central angle greater than 60 degree, would be more than 1cm away...120 degrees in total...(both clockwise and anticlockwise)
so 1 - 120/360 = 2/3 ??

approach? @iLoveTorres

@albiesriram said:
The angle has to be 60 or more
So for each quadrant it comes to 60/360 = 1/6 and for the entire circle shud be 4.1/6 = 2/3
@jain4444 said:
For how many positive integers n are there exactly ⌊n/2⌋ or ⌈n/2⌉ primes less than or equal to n ? ⌊⌋ = the largest integer less than or equal to x.⌈⌉ = the smallest integer greater than or equal to x.
n = 1 to 9 and n=11,13 attributed to the fact that prime numbers occur at higher frequency for the first few natural numbers and then the gap offsets any further possibility.

Hence total 11 such values of n are there.

Team BV -Vineet
@albiesriram said:
10^n=-1 when n is odd
(10+11+12+....+99)-1 +100 -9+8-7+6-5+4-3+2-1
45*109 -5 +100 mod 11
-1-5+1
-5
6?
@pratskool said:
for 1, we have 0 prime number...for 2, we have 0for 3, we have 1 4 we have 2...for every odd number n+1/2 and n-1/2 are least integer greater than equal to and greatest integer less than equal to value of n/2after a certain number, the number of prime numbers start decreasing, for 5 we have 26 we have 37 we have 38 we have 49 we have 410 we have 4...11 we have 4,,,12 we have 5//13 we have 5so we have 1,3,4,5,6,7,8,9 as the numbers which satisfy as the value of n... 8 such numbers..
I think you have missed the word "less than or equal to n"
for n=2, primes

So, n takes all values from 1 to 9,there is a break at 10, which has 4 and 12, which has 5. However n=11 and 13 satisfy with 5 and 6 primes respectively.

Team BV - Vineet
@bodhi_vriksha said:
n = 1 to 9 and n=11,13 attributed to the fact that prime numbers occur at higher frequency for the first few natural numbers and then the gap offsets any further possibility.Hence total 11 such values of n are there.Team BV -Vineet
for n = 2 , we have greatest and smallest integer as 1, but no prime number less than 2(1 is not a prime number).... for 11 we have 5 and 6... no. of prime numbers less than 11 are 2,3,5,7/.. and so for 13...
@pratskool said:
for n = 2 , we have greatest and smallest integer as 1, but no prime number less than 2(1 is not a prime number).... for 11 we have 5 and 6... no. of prime numbers less than 11 are 2,3,5,7/.. and so for 13...
You are making a mistake. Check my above post.

Team BV - Vineet
@bodhi_vriksha said:
You are making a mistake. Check my above post.
yeah, missed it.. thanks
@albiesriram
Is it (c) 6 ?

For first two no's 12 , difference is 1.
for first four no's 1234, diff is 2,
for first 6 no's 123456, diff is 3
.
.
for 100 no's diff is 50

50/11 = 6.
@albiesriram said:
SHud be 6
ďťż




is the ans (d)?
@sur17 said:
is the ans (d)?
Nope. (c) here is the solution by,
@skt. said:
@albiesriramIs it (c) 6 ?For first two no's 12 , difference is 1.for first four no's 1234, diff is 2,for first 6 no's 123456, diff is 3..for 100 no's diff is 5050/11 = 6.
@albiesriram said:
p=0.24^n*0.36
p=0.36(1+0.24 +0.24*0.24+....)
p=0.36(1/0.76)=0.47??

is it option A?